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using C Language on your Amiga
by Dirk Schaun
A Data Becker Boo
Amiga
C for Beginners
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Dirk Schaun
Abacus!
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A Data Becker Book
Fourth Printing, 1990
Printed in U.S.A.
Copyright © 1989, 1990 Abacus
5370 52nd Street, SE
Grand Rapids, MI 49512
Copyright © 1987, 1988 Data Becker GmbH
Merowingerstrasse 30
4000 Duesseldorf , West Germany
This book is copyrighted. No part of this book may be reproduced, stored in a retrieval
system, or transmitted in any form or by any means, electronic, mechanical, photocopying,
recording or otherwise, without the prior written permission of Abacus or Data Becker
GmbH.
Every effort has been made to ensure complete and accurate information concerning the
material presented in this book. However, Abacus can neither guarantee nor be held legally
responsible for any mistakes in printing or faulty instructions contained in this book. The
authors always appreciate receiving notice of any errors or misprints.
AmigaBASIC is a trademark or registered trademark of Microsoft Corporation. Amiga 500,
Amiga 1000, Amiga 2000, Amiga and C64 are trademarks or registered trademarks of
Commodore-Amiga, Inc. Lattice C and Lattice are trademarks or registered trademarks of
Lattice Corporation. Aztec C and Aztec are trademarks or registered trademarks of Manx
Software Systems. IBM is a trademark or registered trademark of International Business
Machines, Inc. Atari ST is a trademark or registered trademark of Atari Corporation.
ISBN 1-55755-045-X
ii
Table of Contents
1. Introduction to C 1
1.1 Program Execution 4
1.2 Compiler vs. Interpreter 5
2. Beginning C 7
2.1 The Editor 10
2.2 The Compiler 11
2.3 The Linker 12
2.4 Putting It All Together 13
3. The First Program 15
3.1 Using ED 18
3.2 Compiling 19
3.3 Error Messages 21
4. Theory and Practice 23
4.1 Program Format 27
4.2 Defining a Function 28
4.3 printf and Escape Sequences 29
4.4 Comments 30
4.5 Variables and Arithmetic 31
4.5.1 Integers 31
4.5.2 The if statement 32
4.5.3 Calculating with C 35
4.5.4 Floating Point Numbers 37
4.5.5 Characters and Character Strings 39
5. Loops 43
5.1 while Loops 45
5.2 for Loops 48
5.3 do while Loops 49
5.3.1 More Error Checking 49
5.4 and and OR 52
6. Strings 55
6.1 Backtracking 57
7. Calculating in C 59
8. Variables 63
8.1 Variable Names 65
8.2 Data Types 67
8.3 Type Conversion 70
8.4 The cast Operator 71
111
9. printf and scanf 73
9.1 More Escape Sequences 75
9.2 Format Specification 77
9.3 Octal and Hexadecimal 80
9.3.1 Conversion Program 82
9.4 Character Codes 84
9.4.1 About the Backslash 85
9.4.2 Going the Other Direction 86
10. The Preprocessor 87
10.1 #define 89
10.2 # include 91
11. Abbreviations 93
11.1 Increment and Decrement 97
11.2 Initialization, Definition, Declaration 99
11.3 Multiple Assignments and Directive Value in C 101
12. Functions 103
12.1 Functions with Arguments 106
12.2 Functions without Return Values 108
12.3 Other Functions 109
12.3.1 strcpy-Version 1 109
12.3.2 strlen Ill
13. Arrays 113
13.1 Multi-dimensional Arrays 116
14. More about Loops 121
14.1 More about the for Loop 123
14.2 break 124
14.3 continue 125
14.4 The switch Directive 126
15. Pointers and Addresses 129
15.1 Addresses 131
15.2 Pointers 133
15.2.1 The Exchange Function with Pointer 134
15.2.2 strcopy-Version 2 135
15.2.3 strcopy-Version 3 135
15.3 Pointer without Storage 138
16. Storage Classes 141
16.1 Auto 143
16.2 Static 144
16.3 External 145
16.4 Register 146
16.4.1 Fast strcpy Routine 147
16.5 Local 149
IV
17. User-defined Libraries 151
17.1 The strcmp Function 154
17.2 Itoa 157
17.3 Reverse 159
18. C Features 161
18.1 The?: Operator 163
18.2 The sizeof Function 164
18.3 Bit Manipulation 165
18.3.1 AND 165
18.3.2 OR 166
18.3.3 Bitwise Shift Operators 167
18.3.4 EXCLUSIVE OR 168
18.3.5 One's Complement 168
18.4 Goto 169
19. Complex Data Types 171
19.1 Struct 173
19.2 Bit Fields 175
19.3 Unions 176
19.4 Enum 177
19.5 Typedef 178
20. Important Concepts 179
20.1 Declarations 181
20.2 Initialization 184
21. Pointer Arrays 187
22. UsefulMacros 193
22.1 Macro Error Sources 196
22.2 Library Macros 198
23. Communication 201
23.1 Passing Data with the CLi 203
23.2 Buffered Input/Output 206
23.3 More Buffered Input/Output 211
23.4 Unbuffered Input/Output 213
23.5 Direct Access 216
23.6 Reading a Character 218
23.6.1 Standard Input/Output 218
23.7 A User Window 219
23.7.1 The Three Windows 219
23.8 Redirection 222
24. TricksandTips 225
24.1 Starting from the Workbench .227
24.2 Other Preprocessor Directives 229
24.3 Finding and Removing Errors 231
25. System Programming 233
25.1 The Intuition Principle 235
25.2 A Window under Intuition 236
25.2.1 The Window Flags 237
25.2.2 Opening a Window 238
25.2.3 A Window Program 239
25.3 Screens 242
25.3.1 A Screen Program 243
25.4 Text/Graphic Window Display 246
25.4.1 Text 246
25.4.2 Move 246
25.4.3 Draw 247
25.4.4 Small Drawing Program 248
25.4.5 Low Resolution and Interlace Modes 252
25.4.6 Pixel Processing 253
25.5 DOS 257
25.6 Set Comment 258
25.7 ReadDirectory 259
25.8 Conclusion 262
Appendices 263
A. Functions 265
B. The History of C 270
C. The Lattice C Compiler 272
D. The Aztec C Compiler 273
E. Reserved C Words 276
F. Operator Precedence 277
G. Storage Classes 278
H. Type Conversions 278
I. Modes for f open 279
Index 281
VI
1
Introduction to C
Abacus 1. Introduction to C
Introduction to C
So you want to learn C. That's obvious, or you wouldn't be reading
this book. The goal of this book is to help you learn to program in C
on the Amiga in as little time as possible. Amiga C for Beginners is
written as a short course in the C language for anyone who wants to
learn about the C language from scratch, without a lot of technical
jargon.
This book is divided roughly into two parts. The first part introduces
the reader to the basic structures of C programming through operating
the editor, compiler and linker. It also contains many sample programs.
You'll be able to write your own short programs in C in only a few
hours.
This first part also takes the beginning C programmer through the
essentials of C — calculations, string handling, loops and more. It even
helps you find the errors made most often by new C programmers.
The second part, which begins at Chapter 10, explains the background
and peculiarities of each C statement and function. These include
preprocessor commands, arrays, loops, pointers, addresses and memory
classes. If these words don't mean anything to you now, they will when
you start reading the second section.
The second part also discusses macros, interfacing your Amiga to the
outside world, tricks and tips for the C language and graphic pro-
gramming.
The appendices describe the history and development of the C language,
as well as operating instructions for a number of popular C compilers
(see your compiler's instruction manual, since many compilers are
constantly being upgraded). In addition, you'll find a number of practi-
cal C functions, mathematical precedence, reserved C keywords,
memory classes and type conversions.
This chapter describes the general nature of C. You'll see its advantages
and disadvantages compared to interpreted languages, as well as advan-
tages and disadvantages compared to other compiled languages. You'll
also see why C stands out above so many other computer languages.
1. Introduction to C Amiga C for Beginners
1 . 1 Program Execution
Before starting we need to ask the big question: "What is C?"
There are two kinds of computer languages. First, there are interpreted
languages such as BASIC and LOGO. Second, there are compiled
languages such as C, Pascal or Modula2. Section 1.2 contains detailed
information about the advantages and disadvantages of interpreters and
compilers.
Compilers Compilers are programs which translate the language statements into a
form understandable to the computer. This form consists of the
numbers and 1 (the numbers used in the binary system). Since people
can't remember long strings of zeros and ones, the computer can be told
to interpret words and other number systems as binary numbers. For
example, a typical machine language instruction LDA means "Load the
Accumulator", which is easier to remember than the binary number
10011101.
The computer must contain a central processing unit (CPU) to respond
to the machine language instruction available in response to every
keyword. Programming with the binary numbers is called machine
language programming. Using machine language mnemonics or
instructions is called assembly language. The instruction which
executes on one computer may not even exist on another computer.
It would be easier for the programmer if the computer could be told in
plain English what to do. Needless to say, computer languages haven't
reached the level of a DWIM (Do What I Mean) interface. This type of
language may exist a few years from now, when technology produces
more helpful developments using artificial intelligence.
High level languages act as a compromise between machine language
and human language. These languages contain a limited number of
statements or keywords which in turn execute specific tasks. Unlike
assembly language, many of these languages aren't tailored to a specific
computer. The computer must execute several hundred machine
instructions for every single statement in the high level language. An
example would be the BASIC command "LOAD Filename", which
tells the computer to load a file.
Abacus
12 Compiler vs. Interpreter
1.2
Compiler vs. Interpreter
An interpreter
A compiler
As previously mentioned, two types of higher level languages exist:
Interpreted and compiled. An interpreter searches for keywords in the
program text (or source), verifies that the command is a legal one and
executes the equivalent machine language instructions. Then the
interpreter searches for the next command, tests it and executes the
machine instruction, etc.
This translation process performed by the interpreter can be compared to
the work of a human foreign language interpreter. An interpreter is a
translator which translates the words of the higher level language into
machine level instructions as needed.
A compiler translates the source program once into executable form.
This is similar to someone who translates foreign language literature
into his/her own language. This translator takes the time to select the
proper choice of words for the text, unlike the interpreter who mediates
a conversation between two people from different language back-
grounds.
The interpreter executes programs immediately. The interpreter can also
be stopped by the user to check on certain values stored in certain vari-
ables. Interpreted program execution can usually be continued without
causing problems. The main advantages of interpreted languages are
flexibility and spontaneity.
The compiler translates the program source only once. The compiler
may spend a few minutes compiling the program before it can be
executed. Afterwards, the compiled program executes much faster than
an interpreted program, since the compiler doesn't have to re-translate
the source program. This advantage becomes most evident in program
loops in which a command can be executed several thousand times. The
interpreter translates the command into machine language, repeating
this process a few thousand times. The compiled program already
knows what to do without repeating the translation. The advantages of
compiled languages lie in shorter execution times for compiled
programs.
Interpreters, because of easy access to their programs, let the program-
mer enter corrections and modifications on the fly. They also let the
programmer enter and execute program code until an error occurs. This
"run-until-it-breaks-then-fix-it" attitude causes lazy, unstructured pro-
gramming style.
1. Introduction to C Amiga C for Beginners
Compilers don't usually allow easy error correction. When an error
occurs, you must reload the program source editor, fix the errors in the
source code and recompile the program. In addition, compiled languages
require a specific language structure, or the program code won't
compile. The source code must be correct from beginning to end or the
compiler will not compile it.
The biggest advantage that C has over other languages is its transporta-
bility. This means that you should be able to take a C source code from
an Amiga, transfer it to a PC, make changes to fit the PC's file
handling and other machine-specific tasks, and compile the C source
code on the PC with no problem.
There you have a general overview of the advantages and disadvantages
of compiled languages and interpreted languages. The next chapter
spends some time talking about these languages as well, while adding
specifics about the subject of this book — the C language.
2.
Beginning C
Abacus 2. Beginning C
2 . Beginning C
Let's look at the process involved in developing a C program. Although
it may seem long and involved, don't panic. Once you learn the basics
of developing a high level language program, it gets easier.
One word of warning: Don't skip this chapter, even if you have
previous experience with C. You might learn something you didn't
know before about the language.
Programs begin with an idea. The user has a task that he wants to
accomplish using a program — and the program should perform the task
easier, faster or more accurately than a human could do it. This idea
could be for a drawing program; a spreadsheet for calculating payroll and
figures; a fast disk copier; or just a simple text display on the screen.
Once the general idea is developed, it helps if the programmer sits down
and Writes out the goals of the idea, and how the program can do this.
This writing stage can be in plain English, since it should be as
readable for you as possible. This written documentation of the program
execution is sometimes called the pseudo code, since it tells what the
program should do without actually writing which statements the
program needs to perform the task. When writing the pseudo code of
this program, keep it broken down into smaller modules whenever
possible.
A data flowchart and program flowchart should be developed from the
written documentation of the idea, just as in any other computer
language. After it has been determined how the program flow should
appear, the user can proceed to the computer to program in the idea.
The C language uses three different programs which work together in
generating programs:
The editor, in which the user enters and corrects the source
program;
The compiler, which compiles the program;
The linker, which joins the main program with other compiled
programs and functions to make a fully executable program.
The rest of this chapter discusses the use of each program in the devel-
opment of C programs.
2. Beginning C Amiga C for Beginners
2.1 The Editor
You need some sort of text editor to enter a C program from the
keyboard. An editor is nothing more than a simple word processor. It
usually contains only minimal text processing capabilities. The
program usually only allows you to type in, load, save and edit the text
of the source code: Nothing fancy lie block functions or save and
replace capabilities.
Most word processor programs can be used for typing in the text of a C
program. If you use a word processor, you may not enter any special
control characters (e.g., bold fonts and text formatting) because the C
compiler would not recognize them. Many word processors provide the
option of letting you save a file as an ASCII file.
If you use a word processor as an editor, it must allow you to enter the
special control characters needed by C source codes. C programs use
braces ({}), brackets (D), the backslash (\), the number sign (#), the pipe
character (I) and the tilde character (~).
Maybe you can't afford a word processor, or maybe your word processor
doesn't have the necessary characters. The Workbench disk which comes
with your Amiga contains an editor named ED. ED is a basic text
editor, which you can find on the Workbench disk of the Amiga from
the cli. Invoke the editor by entering the CLi, typing ed and the
name of the file you want to load/edit, and press the <Return> key.
The editor is loaded and then the C program is typed in. This text,
called C source code, is stored on the disk under a filename. The charac-
teristic that sets this apart from normal word processing files appears in
the file extension: C source codes must contain a file extension of .c.
Examples of names can be sort.c or archive.c; note that these
names indicate the contents of each file. Try to use meaningful names
like this instead of cryptic names like a.c or this.c. The extension of
.C is especially important, since several files with the same name but
different extensions are generated by a C compiler. After a file is created
and saved, you can then call the C compiler to compile the C source
code.
10
Abacus 2.2 The Compiler
2.2 The Compiler
Calling the compiler loads the C compiler into memory. The compiler
reads the source code and begins to convert the source code into
compiled machine language. Most compilers read the source code twice
(two pass compiler). During the first pass, if it encounters an invalid
expression or keyword, it stops compiling and displays an error
message on the screen or writes the error to a disk message file.
Whenever an error is found, you must reload the editor, and correct the
source code. Once you've fixed the errors, you save the source code file,
exit the editor and restart the compiler. If the compiler finds errors
again, you must repeat the above procedures.
Before going any farther, you should realize one thing. Writing the C
source code requires proper preparation. If you just enter source code
without giving any thought to what you're typing in, you'll spend
more time learning about error messages and the editor than you will
spend learning about the C language. In the beginning, prepare to see
plenty of errors, and be patient with yourself as you go from compiler
to editor to compiler.
When you've corrected all of the errors in the source code, the compiler
can finish the first pass without stopping and performs the second pass.
This second pass does the final transformation into object (compiled)
code. The compiler saves the object code to disk under the same name
as the source code, but with an extension of .0. For example, a source
code named source.c generates an object code file named source.o.
The object file needs one more step before it can become executable
program code — this is the linker.
11
2. Beginning C Amiga C for Beginners
2.3 The Linker
We're not done quite yet The object file must still be run through the
linker. The linker searches for all functions used by the program from
the C libraries, and links the necessary functions into one program.
Functions A function is a subroutine similar to a procedure in Pascal. Functions
are capable of solving small tasks such as drawing a line or displaying a
character on the screen. The libraries contained in most C compiler
packages include frequently used functions stored in object (compiled)
form. These functions could be input/output functions, graphic rou-
tines, sound routines or even trigonometric functions.
The linker identifies the functions required for a complete program and
adds them to the main program. This saves a programmer a lot of work.
The functions simply require the passing of values instead of retyping
the source code for each function from scratch.
The C linker permits the development of large programs in modular
form. This means that several parts can be (and often are) developed
separately. The user can compile and test every module separately. This
has the advantage that the complete C program doesn't have to be
loaded and recompiled every time the compiler detects an error. The
linker eventually links all the compiled modules into one complete,
executable C program.
The linker cannot handle non-compiled source code. It can only link
compiled functions together. Source codes can load other source codes
during compilation, but we'll see more on this later.
12
Abacus 2.4 Putting it all together
2.4 Putting It All Together
The CLI The Amiga's CLI (Command Line Interface) is used to specify the
parameters for the editor, the C compiler and the C linker. For example,
entering the following line in the CLI calls the Lattice C linker:
ALINK filel.o file2.o TO complete
You already know that a program may have to be compiled several
times before it is free of errors (syntax errors, not logical errors). You
must enter the above line exactly as written. Entering the line
incorrectly can cause errors in itself. The developers of most C
compilers took this into consideration, and added a special feature to
allow easy linker access from text files.
The MAKE file The inputs required to compile and link a C source code can be written
to a file called a make file. This make file calls all the necessary
programs such as the compiler or linker. The C system reads the file
just as if the user had input the text direct from the keyboard.
It's easy to create a make file. Instead of executing, the C compiler
calls directly. You invoke the editor and write the calls to a script file.
Once you save this file to disk, you now have a make file.
AmigaDOS' Execute command reads this file and passes the informa-
tion to the C compiler sections needed to make the final executable
program. See Appendix C for one example of a make file and its
contents.
13
3.
The First Program
Abacus 3. The First Program
The First Program
The following code is our first C language program. Don't enter it
yet — you'll type it in a few minutes starting at Section 3.1. Here's the
source code so you can see what it looks like:
finclude <stdio.h>
void main ()
{
print f ("Hello, I am here!");
)
To see what the program produces, the text must be entered using an
editor. When you use the editor, please enter the text exactly as it is
printed here and in Section 3.1. This avoids error messages which will
cause problems. Once you've become more comfortable working in C,
you can change programs around to suit your own needs. But don't
change anything until after the program compiles and links exactly as
you see here.
A step by step procedure follows. If you're on the Workbench, you
must start the CLi before anything else. The CLI can be found in the
System drawer located on the Workbench disk. Workbench 1.3 users
can use the shell program, which is an enhanced version of the CLI.
Workbench 1.2 users who can't find the CLI may have it switched off
with the settings in Preferences 1.2. Using Preferences 1.2, you must
click on the ON gadget next to the word CLI. Once you close and
reopen the Workbench disk icon, the CLI icon should appear in the
window.
After you invoke the CLI or shell, a new window appears. This
window prompts for an input with the message:
For a super computer such as the Amiga, this program is something
unusual. No icons appear, the mouse can only be used to move and size
the window, and the CLI only accepts input from the keyboard. Use the
mouse to enlarge the CLI window to its maximum size. Everything
that occurs from now on will be displayed in the CLI window. Now
put the mouse aside — you won't be needing it for a while.
17
3. The First Program
Amiga C for Beginners
3.1
Using E D
First you'll need an editor to enter the program. The ED editor can be
called from the C: directory on your Workbench disk. The following
executes ED and creates a new file named hello.c:
1> ED HELLO.C
The computer places the 1> prompt at the beginning of the line. Some
versions of the CLI may also display the current directory (e.g., the
shell from Workbench 1.3).
The name hello.c will be the name of our first C language program.
It doesn't matter whether you type the name in uppercase or lowercase
letters.
If you made a typing error, press the <Backspace> key to delete the last
character typed. The <Backspace> key has an arrow pointing to the left
on some versions of the Amiga. If you prefer, you can press the
<Ctrl><X> key combination to delete the entire line of text.
Press the <Return> key to execute the command and invoke the editor.
A window appears and displays the text "Creating new file." The user
now enters the program. The editor allows you to move the cursor
around the file using the cursor keys to make corrections and changes.
Type the following text
#include <stdio.h>
void mainO
{
printf ("Hello, I am here!");
)
Once you've finished typing the text, press the <Esc> key, then press
the <S> and <A> keys. Pressing the <Return> key saves the text (this
combination will be called <EscxSA> from here on). Press <Esc>
<XxReturn> to save the text and quit the editor. The system returns
you to the CLI. Pressing <EscxQ> returns you to the CLI without
saving the file. See the book AmigaDOS Inside and Out from Abacus
for more information about ED.
Pressing <EscxXxReturn> returns the user to the CLI window
immediately. You now have your first C source code ready to compile.
18
Abacus
3.2 Compiling
3.2
Compiling
Lattice 4.0 Start the Lattice 4.0 compiler with the following:
1> lc -L hello
For Lattice C 4.0, the following should now appear on the screen. Your
screen may differ slightly. If you get error messages, see Section 3.3.
1> lo -L hello
Lattice Amiga DOS C Compiler Version 4.0
Copyright (C) 1987 SAS Institute Inc. All rights reserved
Compiling hello. c
Module size P=00000014 D=00000012 U=00000000
Total files: 1, Compiled OK: 1
Linking hello
BLink - Version 7.2
Copyright (C) 1986 The Software Distillery.
Copyright (C) 1987 SAS Institute Inc. All rights reserved
Box 8000 SAS Circle, Cary NC 27511-8000 - Telex 802505 (919) 467-8000
Blink complete - Maximum code size = 5488 ($00001570) bytes
Final output file size = 5312 (000014c0) bytes
Aztec C To compile the program using the Aztec C compiler requires two steps.
The Aztec system first compiles the source code then assembles and
links it. A make file can be quite useful. Enter the following for the
Aztec C compiler:
l>cc +L hello
The above sequence may not function in some cases. If not, enter the
same line but omit the +L. Aztec C should display the following on
the screen. Your screen may differ slightly. If you get error messages,
see Section 3.3.
1> cc +L hello
Aztec C68K 3.6a 12-18-87 (C) 1982-1987 by Manx Software Systems, Inc.
Aztec 68000 Assembler 3.6a 12-18-87
1>
Now enter
l>ln hello. o -lm -lc
19
3. The First Program Amiga C for Beginners
Aztec C should display the following on the screen. Your screen may
differ slightly.
l>ln hello. o -lm -lc
Aztec C68K Linker 3.6a 12-18-87
Base: 000000 Code: 001444 Data: 0002a0 Udata:
000050 Total:
001734
1>
Success Did everything work as expected? If you didn't get an error, type the
dir command in the CLI to see the current disk's directory. The exe-
cutable program is stored there under the name hello. Notice that this
file has no extension. There may also be other files with extensions of
MAP, .0, .LNK and of course .C. This shows that the extension helps
identify the file. Call the executable program by entering the following
line:
hello
On the screen appears the text
Hello, I am here!
The program isn't earth-shattering, but this is only the beginning.
20
Abacus
33 Error Messages
3.3
Error Messages
Lattice
The most common mistake a new C programmer makes is omitting the
semicolon following the closing parenthesis of the print f function.
This semicolon is one of the most widely used characters in C
programs since it indicates the end of a statement. For this reason
almost every C statement or function ends with a semicolon. If the user
omits it, the compiler reports many error messages. You might like to
edit the hello.c file again and remove the semicolon. Save the file
and try compiling the file again.
If you forgot to type in the semicolon following the printf function,
the Lattice C compiler displays the following message:
Aztec
hello.c 5 Error 57: semi-colon expected
Compiler returncode 1
The Aztec C compiler displays the following message if the semicolon
is missing:
hello. c:5 ERROR 69: missing semi-colon
1 errors
Let's try to determine from this compiler message what is wrong with
the file. The first line states the filename in which the error appeared:
hello.c. That filename specification is useful later on (more on this
later). Then follows the line number (5), error number (57) and the error
description in English. This indicates that a semicolon was expected in
line 5.
The user must now reload the editor to correct the error:
ED HELLO.C
You must include the extension of .C to edit the C source code.
To reach line 5, you can count down the lines (the fastest method for a
program this short). You can also press <EscxM><5><Return> to
get to line 5. The editor then moves the cursor to the line indicated.
Line 5 consists only of the closing brace (}), but this is expected since
the error actually occurred in the previous line. The semicolon in the
previous line is missing. The error messages of the C compiler should
never be taken too literally, since the search for the error may have to
take the surrounding code lines into consideration.
21
3. The First Program Amiga C for Beginners
After placing the semicolon where it belongs (following the print f
function), save the file again and try to compile the source code again.
It should work.
22
4.
Theory and
Practice
Abacus
4. Theory and Practice
4 . Theory and Practice
Now that you've had some practical experience entering and compiling
a program, let's look at the theory of how the program in Chapter 3
works.
You have two different types of keywords involved in C programming:
functions and statements. The first line contains the function name
void main. The main function is the most important element of a C
program. The void means that this function will not return a value
and is inserted so that the compiler does not display a warning message.
Without this function, literally nothing runs.
Functions A C program usually consists of up to a hundred functions. A function
handles a part of the complete program, and is marked by parentheses 0-
Braces ({}) mark the beginning and end of the function. These braces
surround the statements and functions which the computer should exe-
cute. The following lines call functions:
printf ("Hello") ;
Value (10) ;
music () ;
end ( ) ;
and the following lines don't:
Arguments
value =
music;
end;
old;
If you haven't compiled and linked the program in Chapter 3, do so
now. When you execute the program from the CLi , a jump occurs first
to the main ( ) function. This always happens, regardless of where the
function appears in the listing. It can be at the beginning, middle or end
of the program, but the main ( ) function always executes first. The
main function calls the printf function. The printf function is
stored in a library. All the user needs to know is the function name
(print f ), what it does (displays text on the screen) and what informa-
tion it requires (text).
The information passed to a function during the call are arguments. The
arguments to be passed are placed within the calling function's paren-
theses to ensure proper delivery. It is important to enclose any character
strings within quotation marks (e.g., printf ("Here I am!") ;).
After calling the printf function the text appears on the screen. The
printf function ends and the program continues at the point where it
was interrupted by the function call.
25
4. Theory and Practice Amiga C for Beginners
No other statements follow the line after printf . This means that the
main function has also reached its end, and the program ends. The
computer returns to the CLi, and additional commands can be entered.
The end of the program and the return to the CLI represent the termina-
tion of the main function. The user should note how important this
function is. It represents the C program itself; program execution starts
and ends with the main function.
26
Abacus 4- 1 Program Format
4 . 1 Program Format
Let's discuss the format of the program. The C compiler ignores any
spaces, linefeeds and end of paragraph marks added to the listing by the
user. Indenting lines or adding blank lines helps make source codes
more readable to the user. Formatting has no effect on the execution
speed or the length of the final program. The program you entered in
Chapter 3 could have been in one of the following formats:
void main () {
printf ("Hello, I am here!");
)
void main ()
{
printf ("Hello, I am here!");
)
void main () (printf ("Hello, I am here!");)
It's up to the user to select the version which appears to be most
readable. Once you've selected a style, stick with it. However, the last
version above illustrates how even a small program can be made
unreadable by "formatting" it
Note: All statements and functions must be entered in lowercase since C is
case-sensitive (it differentiates between upper and lowercase letters). If
you entered Printf or printf instead of printf , the linker reports
an error since it cannot find this function anywhere.
27
4. Theory and Practice Amiga C for Beginners
4.2 Defining a Function
A function only executes the statements contained within the braces. If
nothing is written there, the computer does nothing. A program that
does nothing is not very exciting, but it's a good example. The
following C source code compiles without problems (and does
nothing):
void main ( )
O
Don't expect miracles from the above program. When you compile,
link and start it, it loads, runs and does nothing. The computer returns
totheCLl.
Definition The function arguments enclosed in the braces are its definition. It de-
fines what the computer should do when it executes a certain function.
A function can contain several statements or other function calls.
Longer lines of text can be displayed on the screen with this program:
void main()
{
printf ("Hello, I have a question ! \n") ;
printfC'Do you believe in life without electricity?\n") ;
printf ("Not me!\n");
}
The screen output will appear as follows:
Hello, I have a question!
Do you believe in life without electricity?
Not me!
This program has two differences from the program in Chapter 3. First,
there are three printf functions instead of one; second, the \n charac-
ter appears at the end of each string within quotation marks. See the
next section for details on \n and other escape sequences.
28
Abacus 4.3 printf and Escape Sequences
4.3 printf and Escape Sequences
The text at the end of Section 4.2 appears on the screen as it appears in
the source code, with three exceptions. The three \n characters do not
appear. The \n character is called the newline character, one of the
many escape sequences used for controlling the format of text. The \n
character tells the compiler to insert a linefeed at that place in the text,
just as if you pressed the <Return> key.
Any escape sequence can be recognized by the backslash (\) preceding
it. The character following indicates which escape sequence should be
executed. For example, the n signifies a linefeed: The computer starts
the text after the \n at the beginning of the next line.
This newline (\n) escape sequence is important, since the printf
function doesn't automatically add linefeeds after it displays text. You'll
remember that when you ran the program in Chapter 3, the prompt
appeared right after the text. Basically C writes all characters sequential-
ly on the screen, even if they are written with different function calls.
The user must program the function to advance the line.
The user is not obligated to place the escape sequences at the end of the
character string. They can be placed between other "normal" characters
or even at the beginning of the text. If desired, all three lines can be
written within one printf function:
printf ("Hello, I have a question! \nDo you believe in life
without electricity?\nNot me!\n");
This line is rather difficult to read. If you consistently place a newline
(\n) character at the ends of strings, programs will be much easier to
read
The newline character is not the only method of formatting text. The
printf is comparable to the PRINT command in BASIC or the
write statement in Pascal. The f in printf indicates that the text
can be output in a specified format This function can process and dis-
play character strings and other values as specified by the programmer.
Since these capabilities are quite extensive, we'll introduce them to the
reader as needed.
29
4. Theory and Practice Amiga C for Beginners
4.4 Comments
The C language lets the programmer insert comments in the source
code. This can be used to tell the reader what the source code is
supposed to do. Comments have no effect on the speed or size of the
compiled program. Comments start with the / * characters and end with
the * / characters. The compiler skips over everything between the
comment delimeters. Use comments liberally , since they never affect
the final program and add to the readability of the source code.
void mainO
(
/* This program outputs a text which starts */
printf(" Comments — desired — stop — \n") ;
/* hece A and ends over at the opposite end" */
}
Now, think of your first program from Chapter 3. If you added com-
ments to tell a future reader exactly what this program did and when, the
end result could look something like this:
/* Program from Chapter 3 of Schaun's book */
/* Amiga C for Beginners from Abacus (C) 1988 */
/* This program prints the words Hello, I am here" */
/* to the screen. Nothing else. */
#include <stdio.h> /* call standard i/o header file */
void mainO /* main function */
{ /* start of function */
printf ("Hello, I am here!"); /* show text on screen */
} /* end of function */
This is a very exaggerated example. It doesn't matter if you comment a
program this clearly, though — the comments are ignored by the com-
piler.
30
Abacus 4.5 Variables and Arithmetic
4 . 5 Variables and Arithmetic
Our knowledge of the C language is still rather small. Right now you
can display text on the screen and insert comments in source code.
scanf It would be nice to be able to have a program accept input from the
keyboard. The scanf function is the opposite of the print f
function — it reads input instead of displaying output (more about
scanf later).
Consider how a program would execute for questions and answers. First
the print f function displays the question on the screen. Next the
scanf function reads the user's input.
For example, pretend that a number will be input as a response. The
following question asks for a number 1 or 2:
Are you well?
(1) = YES, (2) = NO
Number :
The number must be stored somewhere. C provides a series of variable
types which can be used.
Variable types Variables allow certain types of information to be stored in a computer.
The variable type depends on the type of information you want stored.
There are variables for characters; variables for strings; variables for
different kinds and sizes of numbers; and variables for combinations of
numbers.
4.5.1 Integers
The int variable type represents integer (whole) numbers. Variables of
type int can accept whole numbers from (approximately) -32,768 to
+32,767. The following program uses integer variables, and introduces
a practical application of the scanf function:
/* scanl.c section 4.5 */
void main ()
{
int input;
printfC'Are you well?\n") ;
printfC(l) = YES, (2) = NO\n\n") ;
31
4. Theory and Practice Amiga C for Beginners
printf ("Number: ••) ;
scanf ("%d", Sinput);
printf ("\n\nYour input was: %d\n", input);
}
The first line of the main function, int input;, tells the compiler
what to do with the variables. This line assigns a name to the variable.
The program uses this variable name for access to the variable's
contents. This variable name (input) indicates its purpose. Variable
definition ends with a semicolon.
Format The following lines are the printf functions. Next, the scanf
specification function asks for the user's input in response to the text "Number : "
Since a large number of data types exists, the input routine must be
told what data can be expected. The format specification %d specifies
the data type. Format specifications are similar to the escape sequences
(the characters preceded by a backslash). The percent sign indicates a
format specification; the d tells scanf that the value to be read in
must be of type int. The name of the desired variable follows the
string in quotes, separated from the string by a comma. An ampersand
(&) precedes the variable name. This is important: If the system crashes
the user should first examine the scanf function parameters to make
sure they are correct
If scanf contains the correct information, the user can enter the input
in the running program. Enter a number and press the <Return> key.
This value can be found in the variable input. The program can now
use this number.
This program accepts the input then displays the variable using the
printf function. The printf function must also be told what kind
of data it must process. A format specification identical to the one
which appears in scanf serves this purpose. Because of this, printf
knows that an integer number will be passed, which must be placed at
the location occupied by the format specification in the text. The
variable name input follows the string in quotes, separated from the
string by a comma. The input appears on the screen if Uie input was a 1
or 2 and not text (text is not allowed here). If you enter text, the input
becomes a large random number (in Lattice C) even though this number
never appeared in the input line. If you enter no input scanf scrolls
the screen one line upward and waits for a new (more useful) input.
4.5.2 The if statement
It is rather boring to just let the computer repeat the input It would be
better to respond to the input. For example, have the computer respond
to an entry of "1" with the message, "That is very good!", or an entry
of "2" where the message could be, "I am sorry to hear that!" The
32
Abacus 4.5 Variables and Arithmetic
computer must be capable of comparing the value stored in input
with other numbers. Depending on the results of this test, it must
select one text or the other text. In programming this is known as an
if ...then construct. As in many other languages, C also has this
capability (C doesn't require the then).
The variable is compared with 1. If the condition is found to be true,
the statement following the if command executes. Here is an example:
if (input == 1)
printfC'That is very good!\n");
if (input == 2)
printfd am sorry to hear that!\n");
The conditions appear inside the parentheses so that the first print f
statement only occurs when input equals 1. The same is true of the
following i f statement, with the difference that the text executes if
input equals 2. Semicolons never follow the if.
The user who wants to experiment can try a semicolon after the second
if. If you do so, the program acts as if the line if (input == 2 ) ;
doesn't exist. After each input "I am sorry to hear that!" appears.
Adding the four lines above makes the program run properly, but it
could be improved. Some users may be familiar with the BASIC
statement:
IF A=l THEN PRINT "That is very good! :
ELSE PRINT "I am sorry to hear that ! "
else The C language also has an else statement which can only be used
together with the if statement. The else statement executes only
when the condition has not been met This eliminates the second test.
if (input == 1)
printfC'That is very good!\n");
else
printfC'I am sorry to hear that!\n");
The second test is now improved. A modified version of the C program
now appears as follows:
/* scan2.c 4.5.2 */
void mainO
{
int input;
printfC'Are you well?\n") ;
printf('Ml) = YES, (2) = NO\n\n");
printf ("Input Number: ") ;
scanf("%d", S input ) ;
if (input == 1)
printfC'That is very good!\n");
else
33
4. Theory and Practice Amiga C for Beginners
printfC'I am sorry to hear that!\n");
}
If several commands should be executed after the if (e.g., two
print £ functions), the second line cannot be written immediately after
it. The following example wouldn't work:
if (input == 1)
printf("That is very good!\n");
printfC'Hope you stay healthy ! \n" ) ;/* Not like this! */
else
printfC'I am sorry to hear that!\n");
Statement Since only one line is executed after the if, something else must be
block done. Up to now only one statement has been described. It is time to
describe a statement block. Placing several statements inside braces
creates a statement block which is valid as a unit. This block can be
placed following the if statement without problems:
if (input == 1)
{
printf ("That is very good!\n") ; /* Right! */
printfC'Hope you stay healthy ! \n") ;
)
else
printfC'I am sorry to hear that!\n");
The Amiga can do a lot of things, but what it does best is calculate (and
fast). Let's start with addition. To add two values use the plus sign (+):
sum = number 1 + number2;
The result for this example is stored in the variable sum. This variable
must be defined at the beginning of the function, just like all variables.
Using type int, the following definition results:
int sum
int numberl
int number2
C is a language for lazy people. Most everything can be changed to
abbreviations to cut down on keyboard use. Those who want to become
good C programmers should use this capability. These three variables
are defined as the same data type. You only need to enter int once; all
integer variables can be listed following the single int:
int sum, numberl, number2;
All variables are separated by commas and the list is terminated with a
semicolon.
With this information it's possible to write a program that adds two
numbers. The scanf function permits data input, but this time two
34
Abacus 4.5 Variables and Arithmetic
numbers will be read in. This will not be done with two separate func-
tion calls (this would also be possible), but a second format specifica-
tion is written into the string of the scanf call. It contains %d%d
(notice no spaces) which reads the second parameter. And now the
listing:
/* scan3.c 4.5.2 */
void main ()
{
int sum, number 1, number2;
printf ("Please input two numbers ! \n") ;
scanf ("%d%d", snumberl, snumber2) ;
sum = number 1 + number2;
printf ("%d + %d = %d\n", numberl, number2, sum);
}
The user familiar with other languages such as BASIC can compare the
listings to other language implementations of the same program. The
last printf function with the three format specifications can appear
confusing. The following is a BASIC equivalent:
PRINT "Please input two numbers!"
INPUT N1,N2
SUM = Nl + N2
PRINT Nl;" +";N2;" =";SUM
4.5.3 Calculating with C
The reader can guess what would have to be changed to perform multi-
plication instead of addition. The plus sign is replaced by an asterisk
(*). A hyphen (-) is used for subtraction and a slash (/) performs
division.
Calculations may be performed with constant values as well as
variables. Both constants and variables can be mixed. Some examples
follow to illustrate. It is assumed that all variables are defined and
contain meaningful values:
result = number * 4;
sum = var + 2 + var2 + 3 + var4;
result =4*5-7/ var;
value = 2 * (number - 7);
result =4+5*3-2;
counter = counter + 1;
Evaluating a formula is as simple as entering it into a pocket calcula-
tor. C recognizes the laws of mathematical precedence:
35
4. Theory and Practice Amiga C for Beginners
result = 4+5*3-2;
The result is 17, not 25. The product of 5 * 3 is calculated First, after
which 4 is added and 2 subtracted.
The counter = counter + 1; example above deserves special
attention. This equation is unsolvable for the normal person, but no
problem for the computer. It takes the content of the variable
counter, adds one to it and stores the result in counter. This oper-
ation increments the content of the variable by one for every call.
Let's write a comprehensive program for performing math equations.
The assumptions are that all basic four mathematical functions are per-
formed with two variables. A scanf function reads the numbers. Then
the numbers are tested with several i f statements to determine which
mathematical function should be performed. The result is calculated
accordingly. If an invalid code is input, a message appears.
Here is the finished version of such a program:
/* mathl.c 4.5.3 */
void malnO
{
int numberl, number2, result, operator, error;
printf ("Please input two numbers! \n") ;
scanf ("%d%d", snumberl, s number 2 ) ;
printf ("And now the code for the operation! \n") ;
printf ("l=Add, 2=Subtract, 3=Multiply, 4=Divide\n") ;
scanf ("%d", soperator) ;
error - 1;
if (operator == 1) /* Addition */
(
result = numberl + number2;
error = 0;
}
if (operator == 2) /* Subtraction */
{
result = numberl - number2;
error = 0;
}
if (operator == 3) /* Multiplication */
(
result = numberl * number2;
error = 0;
}
if (operator == 4) /* Division */
(
result = numberl / number2;
error = 0;
}
if (error == 1) /* None of the above conditions */
printf ("Wrong Code! Input only numbers 1 - 4!\n");
else
36
Abacus 4.5 Variables and Arithmetic
printfC'The result is %d\n", result);
}
The program is very easy to read. After all values have been entered, the
variable error is assigned a value of 1. During every operation that
follows, be it addition, subtraction, etc., the error variable is set to
zero. This makes it possible to determine whether one of the four
operations was performed. If this was not true, the value in operator
is illegal.
Before the output, the result is tested to determine if it was calculated.
This can be seen in the variable error.
Test this program thoroughly with various values. Please note that the
integer variables are only permitted to store values between +32,767
and -32,768. Furthermore, division by should be avoided. This would
cause a system crash and a Guru Meditation.
4.5.4 Floating Point Numbers
Perhaps you have noticed something else. Try dividing 9 by 2. The
result displayed by the computer is 4, which is incorrect (4.5 would be
right). Isn't this expensive computer capable of performing correct divi-
sion?
The error can be traced to the variable type. The int variable type is
only capable of processing whole numbers between ±32,000. The value
4.5 is a floating point number, not a whole number. If during a
division a remainder (the fraction after the decimal point) occurs, it is
ignored. This does not mean that the division 9/2 cannot be performed
on the Amiga computer. The only thing required is that the variable
type can be capable of storing floating point numbers. No problem
since C is equipped for this.
float To convert the current program for this new data type, the variables
number 1, number2 and result must be changed. This process
consists only of replacing int with float. The first lines appear as
follows:
main ()
(
float numberl, number2, result;
int operator, error;
This alone is not sufficient since scanf and printf use the format
specification %d which expects an integer value. This is no longer the
case. The %d must be replaced with a %f . The f means a floating point
37
4. Theory and Practice Amiga C for Beginners
value is passed, just like the d is used for integer values. The first
scanf function now appears as follows:
scanf ("%f%f, snumberl, Snumber2) ;
The last print f function must also be changed. The variable
result is now a floating point value. The d is replaced with the f .
Newly compiled and linked, this version makes error free computations
of floating point numbers possible. Numbers stored as type float are
practically unlimited in size. Millions, and even billions and billions,
can be calculated. Here is the complete program:
/* math2.c 4.5.4 */
void main ( )
{
float number 1, number2, result;
int operator, error;
printf ("Please input two numbers!\n") ;
scanf ("%f%f", snumberl, Snumber2) ;
printf ("And now the code for the operation !\n") ;
printf ("l=Add, 2=Subtract, 3=Multiply, 4=Divide\n") ;
scanf ("%d", Soperator) ;
error = 1;
if (operator == 1) /* Addition */
(
result = number 1 + number2;
error = 0;
)
if (operator == 2) /* Subtraction */
<
result = number 1 - number2;
error = 0;
}
if (operator == 3) /* Multiplication */
(
result = number 1 * number2;
error = 0;
)
if (operator == 4) /* Division */
(
result = number 1 / number2;
error =0;
}
if (error == 1) /* None of the above conditions */
printf ("Wrong Code! Input only codes l-4!\n");
else
printf ("The result is %f\n", result);
>
Lattice The library for mathematical functions and floating point numbers must
be linked with the standard library. Example:
lc -Lm math2
38
Abacus
4.5 Variables and Arithmetic
Aztec
If you work with the Aztec C compiler, the library for mathematical
functions and floating point numbers must be linked with the standard
library c.lib.
Example:
cc +L math2 .c
In math2 . o -lm
•lc
4.5.5
Characters and Character Strings
char
Besides the int and float variable types which accept numbers, you
need another category of variables to store characters. It would be better
if the program above could accept a plus sign instead of the number 1
to indicate addition. The data type char allows variables to be defined
which can accept characters.
The syntax for definition of a char variable is exacUy as described in
the float and int variables:
char character;
This type of variable has its own format specification for the printf
and scanf functions. A c is used for the type char. To give the
calculation program a few extras, the operator is entered as a character.
This means that instead of entering a number as you had to before, you
can enter a math operator instead.
Another improvement can be made at this point The format for
entering equations should be similar to that of a pocket calculator (i.e.,
first number, operator, second number). You should be able to press the
<Return> or <Enter> key instead of the <=> key. Since the scanf
function is so flexible, the following change is sufficient to make this
possible:
scanf ("%f%c%f", Snumberl, soperator, S number 2 ) ;
The %c between the two format specifications indicates character input.
The tests which formerly checked the code now have to test the charac-
ters for the operators. Nothing easier than that! Only the characters
must be placed in apostrophes (single quotes):
if (operator
• + ')
39
4. Theory and Practice Amiga C for Beginners
After all the small changes, compare this version to the final program
below in which some other cosmetic changes were made. The reader
should now be able to understand the additions made.
During the input a small item has changed. Until now the <Return>
key had to be pressed (but not required) after inputting each number.
Now the entire input must be in one line. The reason for this is the fact
that a single character is read in with %c. This could be a <Return> or a
space. For this reason the first number is followed immediately by the
operator after which the <Return> key may be pressed, if desired.
Finally the second number appears as in this line:
15.500000 * 12.500000 = 193.750000
Here is the final version of this program:
/* math3.c 4.5.5*/
void main()
<
float numberl, number2, result;
char operator;
int error;
printf ("Input Format: Number, Operator, Number (no
spaces) ! \n") ;
scanf ("%f%c%f", snumberl, Soperator, Snumber2) ;
error = 1;
if (operator == •+') /* Addition */
{
result = numberl + number 2;
error = 0;
>
if (operator == '-') /* Subtraction */
{
result = numberl - number2;
error =0;
}
if (operator == •*') /* Multiplication */
{
result = numberl * number2;
error = 0;
}
if (operator == •/') /* Division */
{
result = numberl / number2;
error = 0;
}
if (error == 1) /* None of the conditions above
satisfied? */
printf ("Wrong Operator %c!\n", operator);
else
printf ("%f %c %f = %f\n", numberl, operator, number2,
result) ;
)
40
Abacus 4.5 Variables and Arithmetic
Lattice The library for mathematical functions and floating point numbers must
be linked to the standard library. Example:
lc -Lm math3
Aztec If you work with the Aztec C compiler, the library for mathematical
functions and floating point numbers must be linked with the standard
library c.lib. For example:
cc +L math3.c
In math3.o -lm -lc
41
Abacus 5. Loops
5. Loops
The programs presented up until now execute straight from beginning
to end. An if statement may skip over some spots, but we haven't
jumped to earlier statements. Loops branch to earlier sections of the
program.
5.1 while Loops
The while statement is followed by two parentheses which surround
the desired arguments. An example makes this clear:
void main()
{
int counter;
counter = 15;
while (counter > 0)
{
printf ("Counter is %d\n", counter);
counter = counter - 1;
)
The block which appears after the while statement executes until the
conditions inside the parentheses are true. In the beginning, the variable
counter is set to 15. While the condition counter > has been
met, the following block is executed which outputs the current value of
counter and then decrements it by one. In this case the printf
function is called 15 times until counter has been reduced to 0. The
conditional statements can be formed by using tests for equality (=),
greater than (>), less than (<), greater than or equal to (>=), or less than
or equal (<=). The comparison here is for counter to be greater than
0.
The comparison operators for C are similar to those found in most
programming languages.
45
5. Loops Amiga C for Beginners
< less than
<= less than or equal to
> greater than
>= greater than or equal to
= equal to
!= unequal
Instead of
while (counter > 0)
the following could be written:
while (counter >= 1)
The latter is preferred since the limit is explicitly provided. To construct
a loop which counts up to the value 100, it is recommended to use this
number in the test.
while (counter <= 100)
In the comparison operators <= and >=, the equal sign (=) always
appears at the end.
Factorials A practical example is the calculation of a factorial number through
constant multiplication. A factorial in mathematics is the product of all
whole numbers up to a set value. The factorial of 4 therefore is:
4! =1*2*3*4= 24
Here is our example program:
/* factorial. c 5.1 */
void main()
{
int num, i;
float factorial;
printf ("Please input a number: ") ;
scanf ("%d", Snum) ;
i = num;
factorial = 1; /*Initialize */
while (i >= 1)
(
factorial = factorial * i;
i = i - 1;
}
printf ("%d! = %f\n", num. factorial);
)
46
Abacus
5.1 while Loops
Lattice
Aztec
Now for a few hints in helping you compile this program with your
compiler.
The library for mathematical functions and floating point numbers must
be linked with the standard library. Example:
lc -Lm factorial
If you work with the Aztec C compiler, the library for mathematical
functions and floating point numbers must be linked with the standard
library clib. Example:
cc +L factorial. c
In factorial. o -lm -lc
47
5. Loops Amiga C for Beginners
5.2 for Loops
Another loop can be constructed using the for statement. In BASIC
the command is used as follows:
FOR I = to 100 STEP 2
NEXT I
In C this appears as follows:
for(i = 0; i <=100; i = i + 2)
C doesn't require a NEXT as in BASIC, since only the statement block
following the loop header is executed. Within the parentheses are some
interesting items. There are three individual statements separated from
each other by semicolons. A semicolon does not follow the last entry.
The loop body ends here with the closing parenthesis. The first entry
i = assigns a starting value to the variable which is modified within
the loop. The statement i <= 100 represents the ending condition.
Until it is satisfied, the loop executes. The last part of the loop body
increments or decrements the control variables which were previously
initialized with a starting value.
48
Abacus 5.3 do while Loops
5.3 do while Loops
The last type of loop is the do while loop. The reader has already read
about the while loop; this loop is quite similar. Please compare the
two program sections below:
/* first program section */
while (i > 0)
{
i = i - 1;
printfC'i is %d\n", i) ;
)
/* second program section */
do
{
i - i - 1;
printfC'i is %d\n", i) ;
} while (i > 0) ;
The do begins the do while loop, and the while ends the loop.
This leads to a small but significant difference in program execution. In
the first example the program checks if variable i is still greater than
and then executes the loop only if the conditions are met. In the second
example the test is executed only after the loop has already been
executed once. If i contains the value 0, the while loop is skipped,
unlike the do while loop which executes at least once.
Please notice the semicolon which must follow the while. It is often
forgotten since normal while loops don't use semicolons.
If this material is not clear without further example programs, the user
is encouraged to write some short programs (e.g., which output the
values of the variables used).
5.3.1 More Error Checking
The next section deals with error detection. Up to now it was difficult
to make mistakes, except for errors in typing. When the program sud-
denly reports errors, there's no need to panic. Study the messages the C
compiler returns. You may have to do a little thinking to detect cleverly
hidden errors.
49
5. Loops Amiga C for Beginners
Find the Below is a new program. Based on what you know so far you should be
errors able to determine where the errors are hidden, and which lines could
cause problems. The listing contains errors which result in a long series
of error messages. Try to find the hidden errors on your own first. Fix
these errors, then try compiling the source code to see what you missed.
We've included the solution directly after the listing. The program
should add all numbers from 1 to 100 and display the subtotals and the
final total on the screen.
main ( ) ;
{
printfC'I add all numbers from 1 to 100/n") ;
i = l;
do
printf ("Subtotal for %d. value: %d/n", i, sum);
sum = sum + 1;
i-i+1;
while (i < 100)
printf ("Sum of all numbers to 100 is %d/n", sum) ;
>
Did you find all the errors? You should have found most of them, since
the program is almost completely wrong! Even if you found no errors,
you can follow the remaining material without problems.
Let's start with the first line which contains an error (of course). The
semicolon following main shouldn't be there. The missing void only
results in a warning, not an error. The next line with the brace is correct
(an exception in this program). The compiler accepts the first printf
function without problems. It doesn't contain a syntax error. The line
would even be right if you wanted to display the slash (J) and an n. The
slash (/) should have been a backslash (\). To be consistent, this error
occurred in all the printf functions in this program.
The assignment i = 1; is correct. The do while loop, which should
execute the following three lines, has no braces (the braces make the
three lines into a statement block). The semicolon is also missing after
the while (K100) line.
Within the loop, the values for i and sum should be displayed. Except
for the error with the escape sequence \n everything is correct here.
Finally the program increments the contents of sum and i are incre-
mented. Trouble is, the sum variable was never defined. The C com-
piler doesn't know what is meant by i and sum. A line must be added
before the printf function.
int sum, i;
Before or after i = 1;, a sum = 0; must be added. After these changes
the C compiler is happy but the program will not display the right
output. There are still two logical errors in the program. The first
50
Abacus S3 do while Loops
occurs as the subtotal is displayed. The value of sum is displayed before
it has been calculated. The line sum = sum + i; must be placed before
the line with:
printf ("Subtotal for %d. value: %d\n", i, sum);
The while test remains which terminates the program after the num-
ber 99. The change is simple:
} while (i <= 100);
The error free version of the program appears below:
/* errorfree.c 5.3.1 */
void main ()
{
int sum, i;
printf ("I add all numbers from 1 to 100\n") ;
sum =0;
i = 1;
do
(
sum = sum + i;
printf ("Subtotal for %d. value: %d\n", i, sum);
i = i + 1;
} whileU <= 100)
printf ("Sum of all numbers to 100 is %d\n", sum);
)
51
5. Loops Amiga C for Beginners
5.4 AND and OR
Up to this point, only one exit condition can be checked in your loop.
This changes with the introduction of the && and I I operators. The <l>
key can be found on the right side of the keyboard above the <Return>
key. The & & represents the logical and and the I I the logical OR.
Why these operators are called logical will be revealed later since other
logical operators also exist in C. From BASIC the commands and and
OR are familiar and they are the same as the operators in C.
and Connecting two conditions with and:
while (i <= 10 && i >= 5)
The loop is now executed when
i is less than or equal to 10.
i is greater than or equal to 5.
If one of the two criteria is not met (e.g. i = 4), the entire condition is
false and therefore not satisfied. Only if both tests are true can the loop
be executed.
OR OR is used as it is in daily conversation. If one of the two conditions is
true, the entire expression is true. The next example assumes that a
character variable should be tested for a certain content. Since the logi-
cal connections can be used with other conditional tests, they can be
used together with if:
if (operator == •+■ || operator == '.' || operator == '*'
I I operator == ' / ' )
printfC'The operator is valid!\n");
Four tests were made, of which only one must be true. If several tests
can be positive, this is no problem since only one true condition is
sufficient That the if statement could be written in two lines should
be nothing new. Remember that the formatting of the C listing is of no
interest to the C compiler.
Negation There is another operator to be discussed. This is the negation operator
! , mentioned as a part of the inequality operator ! =. With this character
all tests and returns can be made into the opposite. If a test should be
made to determine if a character is not an arithmetic operator, the fol-
lowing test can be devised:
52
Abacus 5.4 AND and O R
if( !( operator == '+■ II operator == ' . ' II operator ==
'*' II operator == •/'))
printf("Not a valid Operator !\n") ;
All tests are made within the parentheses. If the expression inside the
parentheses is true, a valid character is present, the negation operator
goes into action. It simply reverses the matter. From the true test it
makes a false one so that die printf command is not executed. This
is similar to the false test result within the parentheses, when none of
the signs + - * / are stored in the variable. In this case the ! operator
makes it a true test That is the same procedure as inserting a not into
a sentence. In everyday English double negatives can be used in one
sentence, but not many people will understand it.
53
Abacus 6. Strings
6 . Strings
You've entered strings and displayed them on the screen in previous
chapters. What else can you do with them? The following code shows
string variable definition:
char name[number_of_fields] ;
Strings consist of groups of individual characters of type char. The
above variable definition tells the compiler the maximum number of
characters the string can have. If you want to process a single character
belonging to the string, you can't just call the variable — you'll get the
entire string. In addition, you must know the exact location in the
string at which you can find the specific character. You'd enter the
number of the character in brackets, just as you did in the definition.
Let's take the first character in a string. This first character appears in
the first position of the string, and is assigned position (computers
always start counting with 0). All locations then shift by one. The
second character can be reached using the value 2, due to the index,
which acts as a position indicator. Every position contains a character.
All characters are arranged sequentially in a large or small string.
6.1 Backtracking
Let's write a program which displays the text backwards on the screen.
Before starting, you must assume mat a string can be any length. The
string will always end with the value (null). The last character of the
string must be processed first if you want the text displayed backwards.
The program needs a small for loop to find the last character of the
string (0):
char input ( 81 ] ;
int index;
for (index = 0, input [index] != 0; index = index + 1)
The loop body (the statements executed during every pass through the
loop) is empty. A single semicolon follows the for loop. Since a
block of statements follow every loop, this semicolon ends a block that
57
6. Strings Amiga C for Beginners
does nothing. This is the empty statement. The data in parentheses
perform all die required operations. First the index is set to 0. Then the
test follows which determines whether a character is not equal to 0. If
the condition is satisfied, the index is incremented by one. The last
element of the string contains a zero and the loop ends. The result in
index is the length of the string. The last character of the string is
located one position before the null value. Therefore the index variable
must be reduced by one before being used. The index counts down to
zero one step at a time and the program displays a character at every
step.
do
<
index = index - 1;
printf("%c", input [index];
} while (index > 0) ;
You now have the information you need to write the entire program.
One other item before you enter and compile this program: If you have
the Aztec C compiler, this program will not compile using the +L
(longwords) option. Omit this option when compiling this program
with Aztec C. Here's the source code:
/* backwards. c 6.1 */
void main ( )
{
char input [81] ;
int index;
printf ("Please input some text!\n");
scanf("%s", input); /* Strings do not require & */
for (index = 0; input [index] !=0; index = index + 1)
; /* Search for End mark! */
printf ("Your input >%s< has %d characters\n", input,
index) ;
do
{
index = index - 1;
printf ("%c", input [index] ) ;
} while (index > 0) ;
printf ("\n\n") ; /*Blank line before Prompt */
)
Enter a string of characters, but do not include any spaces. The for
loop calculated the length of the input string and then the do while
loop printed it out backwards. Former BASIC programmers may
remember the len function. In C, the user can easily create a function
or routine to do this.
58
7.
Calculating in C
Abacus
7. Calculating in C
7.
Calculating in C
You have already seen how fast the Amiga computes; addition (+), sub-
traction (-), multiplication (*) and division (J) are familiar to you.
Modulo The modulo operator (%) performs another mathematical operation —
operator modulo division, which calculates the remainder of an integer division.
The result is assigned to a variable using the equal sign, where the
variable must be to the left of the assignment operator. The general
format is as follows:
Variable = operandi <> operandi
(<> represents the operator)
First the program calculates the expression to the right of the equal sign
and places the result in the variable to the left of the equal sign. Because
of this, statements such as the following are possible:
variable = variable + 1;
This expression is impossible in normal math, but poses no problem
for the computer. The computer reads the variable content, adds one and
stores the result in the same variable. Combinations of math operations
are possible as the following examples show:
number = 3 * 32
number =2+6*7
number = 5 * (180/3
number = number - 1
number = number % 2;
+ 9)
(5 - 2)
Precedence Division and multiplication have precedence over addition and subtrac-
tion. This rule is also observed by the C compiler. Therefore, the
expression 2 + 6*7 needs no parentheses to achieve the correct result
The modulo operator has precedence equal to division, and therefore
precedence over subtraction and addition. Example:
5 % 3 = 2, since 5/3=1 and remainder is 2.
Simple calculations don't need to use a variable. The following pro-
gram will illustrate:
void mainO
{
Int number;
number =3 * 12;
printf ("Result: %d\n", number);
}
61
7. Calculating in C Amiga C for Beginners
A variable does not have to be used in this program since the %d char-
acters tell print f that it can expect an integer value. The term 3 *
12 can be passed directly to the function as a parameter. The calculation
of the result occurs before the value is passed so no variable is required.
The following program is faster and shorter
main ( )
{
printf ("Result: %d\n", 3 * 12);
}
An integer number can contain only a whole number, so the statement
number = 3/2 places a value of 1 in the variable number. The
correct result would have been 1.5, but the result will be rounded to the
next whole number.
Note : The number -2.25 is rounded to -2 and not -3 since -2 is larger than -3.
Lattice C rounds numbers toward 0, but this can differ with other C
compilers. Only a test run helps to explain what happens with -5 / 2,
in which either -2 (toward zero) or -3 (rounded) appears as a result
62
8.
Variables
Abacus 8. Variables
8 . Variables
The earlier chapters used variables. These are areas of memory used for
storing mathematical results, as well as different kinds of data.
Variables are subject to certain rules and regulations. They must be
assigned specific data types and unique names. As you'll see in this
chapter, there are many types, and the names can be almost anything
you want them to be.
8 . 1 Variable Names
The names given to variables must follow some rules. The following is
a list which describes these rules:
1. The first character must be a letter (the underscore character [J
counts as a letter); after the first character, any legal character can
be used.
2. Characters within variable names can be letters, numbers or under-
score characters (the shifted minus sign).
3 . No control characters or foreign characters allowed.
4. Variable names can be of any length, but many C language com-
pilers use only the first eight characters of the variable name (the
Lattice C compiler permits up to 30 valid characters, Aztec up to
31 characters).
5 . Reserved C keywords may not be used as variable names.
6. Variable names are case sensitive (i.e., the compiler sees a differ-
ence between upper and lowercase).
Some examples are shown to make these rules more understandable.
Some are correct and some aren't. Can you find the bad names?
65
8. Variables
a)
Number_l
b)
c)
2__pi
first-var
d>
Book_no_l
e)
f)
Book_no_2
int
g)
h)
_flag
int_valu
i)
number_l
J)
secret_Password
Amiga C for Beginners
The following variable names are correct: a), d), e), g), h), i) and j). It
should be noted that a) and i) are different variables since upper and
lowercase letters are differentiated, d) and e) may refer to the same
variable on some C compilers, since the names are the same for the
first eight letters. Errors would occur on some C compilers since these
variable names are longer than eight characters: c), d), e) and j). h) uses
a C keyword as a variable name, but this is permitted since the rest of it
doesn't match the keyword.
Look at examples b), c) and f). The variable in b) starts with a number
(not allowed). A hyphen appears in c) (the hyphen is considered a
special character). Finally f) uses a variable name which is a reserved
keyword of C.
The following list shows the reserved words used in C:
auto
enum
short
break
extern
sizeof
case
float
static
char
for
struct
continue
goto
switch
default
If
typedef
do
int
union
double
long
unsigned
else
register
void
entry
return
while
66
Abacus 8.2 Data Types
8.2 Data Types
Until now three data types have been described: int, float and char
(strings).
int Integer values are type int. The 16-bit int type represents whole
numbers between -32,768 and 32,767. The int type works well for
general use. The Amiga libraries use 32-bit integers, but for portability
of your source code to other computers you may want to use 16-bit
integers.
float Floating point numbers are assigned the data type float. A float
variable can store extremely large or small numbers, and numbers with
decimal places. In this type of variable the values can be presented in
scientific notation. Very small numbers such as 0.00000015 can be
written as 15E-7 (the use of E is an abbreviation). 15E-7 is scientific
notation for:
15 * 10"
Numbers with as many as 15 places can be written. The "e" which
separates the exponent (here -7) from the mantissa (in this case 15), can
be written in upper or lowercase letters. In both cases that compiler will
translate it without problems.
Even the float variable type has its limitations. The largest number
permitted is 10 38 . Any number less than 10" 38 converts to a 0. The
value 10 40 when written out is a number which has a decimal point, 39
zeros and a one, in that order. The computer views it as 0. Floating
point variables remain accurate up to seven decimal places. Try the
math3.c calculation program from Section 4.5.5; enter the number
16.8. The program converts the number to 16.799999.
double If you need more accuracy, use the double variable type. Variables of
type double are about twice as accurate (11-14 decimal places).
However, double variables require more memory.
There are times when float and double variable types don't have
the accuracy of integer values. On the other hand, rounding numbers off
can cause incorrect results in multiple calculations. The result becomes
more inaccurate with every additional operation.
Avoid comparing a fixed value during a test. For example:
if (value == 1.0) /* Not like this */
67
8. Variables Amiga C for Beginners
It would be better to test if it is larger or smaller so that the value tested
is not skipped through a rounding error. Otherwise an infinite loop
could result
Special conditions must be considered when using floating point num-
bers. To determine if a constant without fractions following the decimal
point (for example 2) is a floating point number, another digit must be
added after the decimal point This error occurs during the printf call
in the following example:
printf ("Result of 2 / 3 = %f.\n", 2/3);
The example computes 2/3 as an integer value and passes as a result
The function waits for a floating point number which was indicated by
% f . The example below is the correct version:
printf ("Result of 2 / 3 = %f.\n", 2.0/3.0);
Note: You may crash the system as well as get the wrong answer with the
example above. If you want to try the two examples above, save any
important data you might have on the RAM disk to a floppy disk
before continuing.
char Other data types can be derived from the basic types int and float.
For example, the type char which can accept a character is really a
variable for whole numbers between -128 and 127. This small relative
of int represents the ASCII values of the characters.
long The long type is another type derived from int. Long accepts inte-
gers between -2,147,483,648 and 2,147,483,647. If you must define
constants as long values, place an 1 or L behind the floating point
number instead of .0. For example:
1L
sh ort The C keywords unsigned and short can be used as adjectives to
the basic types. These specify integer values. The combinations of
unsigned and short cannot be used with float values,
unsigned defines an integer number which has no sign; short
accepts only 16-bit numbers.
If the indication of int or float is missing, C defaults to int. The
following combinations are valid:
unsigned = unsigned int
short = short int = (Compiler dependent) char
long = long int
unsigned long int
long float = double
68
Abacus 8-2 Data Types
The advantage of unsigned is limited to positive values, and extends
the limit of the normal type. For example, unsigned int accepts
numbers between and 65,535. The normal int type only permits
positive values up to 32,767. Unsigned numbers also allow operations
which cannot be performed with other types. More on this later.
The value assignment to char variables proceeds in the following
manner, as in int values:
char character;
character = 65;
char stores characters. This is done with the following assignment
which leads to the same result as the line above.
character = 'a';
The combination of integer values with the attributes short, long
and unsigned return different results from one compiler to another.
For this reason no general value or memory requirement can be pro-
vided. The following relationship exists between the length of variables
used by all C compilers:
char <= short <= int <= long
The table below describes the length of the different numeric variable
types:
T.at.t i ce
A7tec
char
1 byte
1 byte
short
2 bytes
2 bytes
int
4 bytes
2 bytes
long
4 bytes
4 bytes
69
8. Variables Amiga C for Beginners
8 . 3 Type Conversion
Type conversions sometimes become necessary during computation
because of the use of various data types. The following rules govern
type conversion:
1. char and short always convert to int; float always con-
verts to double.
2. If after these conversions one of the operators should have the type
double, the second operand and the result also convert to
double.
3. If a data type is now long, all participating values also convert
to long.
4. If an unsigned value exists among the operands, all values
convert to unsigned.
70
Abacus 8.4 The cast Operator
8.4 The cast Operator
Constants, function values and variables can be converted into a specific
data type. The parameter to be converted is placed in parentheses and is
preceded by a data type in parentheses. This is the cast operator. The
parentheses are not always required, but are recommended because of the
high precedence of the type conversion. For example:
long number;
number = 123 / (long) ('a' / 1.5);
In a general format, the expression is:
(type) Parameter
Better format:
(type) (Parameter)
Any data type can be substituted for the word type.
71
9.
print f and
scanf
Abacus 9. printf and scanf
printf and scanf
The most powerful output function in C is printf. You've seen a
little of what it can do with screen output using examples printed earlier
in this book.
The scanf function gives the user the option of input to the com-
puter. You have had a chance to work with this function as well.
Both scanf and printf use a number of format specifications and
escape sequences for controlling the format and type of input and
output.
9 . 1 More Escape Sequences
You'll remember reading about the \n escape sequence in Chapter 3.
The following list shows other escape sequences, which you'll find
useful for controlling text output.
\t places output at the next tab stop (all 8 positions)
\b moves the current write position one place to the left (backspace)
\ r inserts carriage return at first position of the current line
\ n inserts carriage return and linefeed
\ f inserts form feed
\ \ prints the backslash character ft)
\" prints quotation mark within the string
\ ' prints apostrophe within the string
\nn prints any character with the octal value nn
Note : An escape sequence uses two characters in the text, but represents only
one character. Keep this in mind when calculating memory usage.
The following program uses the \t escape sequence for tab stops:
main ()
{
printf (AnXtExample, \ttwo\tTabs\tspacing") ;
printf ("\tspacing\tText !\n") ;
}
For our next assignment we wish to display the following text
Use the control characters : "\n", "\t"!
75
9. PRINTF AND SCANF AMIGA C FOR BEGINNERS
It is not possible simply to place the text in quotation marks since they
already occur in the text Escape sequences are necessary. The program
prints the quotation mark using the \" escape sequence, the backslash
with \ \. The necessary printf call appears as follows:
printf ("Use the Control Characters: \"\\n\",\"\\t\" ! ") ;
Here is an example program:
main ( )
{
printf ("Small ") ;
printf ("\"T est progra m") ;
printf ("\"\n\nWhere\nis the\ntext now?\n") ;
printf ("XtEverything OK?\n") ;
>
The output is:
Small "Test program"
Where
is the
text now?
Everything OK?
76
Abacus
9.2 Format Specification
9.2
Format Specification
Strings can accommodate format specifications as well as text and
escape sequences. Every format specification has a corresponding vari-
able attached to the string and separated from the string by a comma.
The format specifications always start with a percent character (%) and
can be used in the print f and scanf functions.
A difference from the format string of the print f function is impor-
tant: The scanf function reads in data. For this reason the escape
sequences \n (linefeed), \t (tab) and space divide the input into sepa-
rate fields.
Here is a table with format specifications for printf and scanf:
Format specification Data type
char (one character)
integer value
string
float and double number (for printf
output with format [-]xxx.xxxxxx)
integer value as octal number (base 8)
integer value as hex number (base 16)
unsigned integer value (printf only)
float or double output (printf only) in
scientific notation [-]x.xxxxxxE[+-]xx: affects
scanf asin %f
shortest form of %e and %f (printf only)
short (scanf only)
represents the % character (printf only)
%c
%d
%s
%f
%o
%x
%u
%e
%g
%h
Additions The integer elements d, u, o and x can be preceded by the letter 1 to
indicate that long values instead of integers are used. Long values are
integers of double length. An 1 preceding floating point numbers con-
taining e, f and g indicates that double values are expected. The field
width of the input or output of a field can also be indicated with a
format element. After the percent sign, the size of the individual field
can be indicated. If the first character of this number is a minus sign,
the text is left justified. Spaces fill the remaining positions in the field.
Without indication of the field width, the standard setting for %f in the
printf function is %.6f . The output therefore always has six decimal
places and any field size.
printf and elements for float values:
%<min>.<fraction>F
77
9. PRINTF ANDSCANF AMIGA C FOR BEGINNERS
<min> indicates the minimum width of the output field.
<f raction> is the maximum number of numbers after the decimal
point. F is one of the format specifications e, f or g. The indication of
for fractional positions truncates all numbers after the decimal point
(e.g., %.0f). For example:
printf ("Number %5.21f\n", 12.345);
creates the output:
Number 12.35
In this case the program expects a double number (If) at least 5
characters wide, but with only 2 decimal places. Since rounding is per-
formed to the second number after the decimal point, the number 5
appears at the last position. If less numbers are available than the num-
ber indicated for positions after the decimal point, zeros are attached.
printf and elements for integers:
%<Min>F
<Min> indicates the minimum width of the output field. F represents
one of the format instructions d, u, o or x. Example:
printf (">%4d<", 12);
Output:
> 12<
printf and %s:
%<Min><real>s
<Min> indicates the minimum width of the output field, while
<real> describes the actual number of characters displayed. The fol-
lowing examples show the effects on the string "Sampletext":
Format Specification Output
>%6s< >Sampletext<
>%-6s< >Sampletext<
>%12s< > Sampletext<
>%-12s< >Sampletext <
>%12.6s< > Sample<
>%-12.6s< >Sample <
>%.6s< >Sample<
The scanf function is much simpler. Only one number exists which
indicates the maximum input length possible. As soon as a character no
longer fits into the format of a data type, or a control or blank character
appears, the input for the current field ends. This means that during
78
Abacus 9.2 Format Specification
input only characters representing an integer number are used. If other
characters are input, the integer number input ends. In addition '*' can
be used which precedes the format instruction for data type and sup-
presses the assignment. The field is simply skipped in this case.
int i;
float f;
char string [50 ];
scanf(%3d %f %*d %s", si, if, string);
Input: 1234567.89 12345all clear?
Value i contains 123, since the field should have 3 places, and only numbers
assignment can appear. The value 4567.89 is in f , because the space after "9" pre-
vents additional reading of input. The same happens after the storage of
"all" in the stringQ. The number sequence "12345", which normally
is assigned to an integer value, was skipped because of the asterisk.
This means that with the scan £ no spaces can be read. This makes
scanf less than ideal for string input
If the reader can't remember all of this material, don't worry. It is used
intensively during the course of the format specifications.
79
9. PRINTF AND SCANF AMIGA C FOR BEGINNERS
9 . 3 Octal and Hexadecimal
Two number systems are used often in C. To discuss these systems,
we'll start by looking at the decimal system. Let's take a decimal num-
ber and dissect it into its component parts:
5279
5,000 + 200 +70 +9
5 * 1,000 + 2 * 100 +7* 10 +9*1
5 * 10 + 2 * 10 + 7 * 10 1 + 9 * 10°
This makes the origin of the term decimal = 1 in our number system
clear. Every number position has a certain value. There are ones, tens,
hundreds, etc. The value of these positions is multiplied with the num-
ber at that location. For example 7 * 1 0. The factors 1, 10, 100, 1,000
can be traced again to the base 10. The exponent in base 10 depends on
the position of the digit in the number. The first position corresponds
to exponent 0, the second exponent 1, the third 2 and so on.
Numbers between to 9 can be used, which makes ten different num-
bers available. This is the reason the system is called base 10.
Octal system If you used eight different numbers (0-7) instead of ten, the base in the
calculations would be 8. This base 8 system is better known as the
octal system. The following example shows the process of calculation a
number in the octal system. To differentiate the different number sys-
tems, the base number appears in subscript or in parentheses following
the number:
6204
3
= 6*8
2
+ 2*8
+ 0*8
+ 4*8
= 6 * 512
+ 2 * 64
+ 0*8
+ 4*1
= 3,072
+ 128
+
+ 4
= 3,204
10
This brings us back to the format specifications. To write a variable in
octal on the screen, use %o.
printf("3204 dec. = %o octal\n",3204) ;
80
Abacus 9.3 Octal and Hexadecimal
Hexadecimal The format specification %x converts a number into the hexadecimal
system. As the name suggests, hexadecimal is base 16. This produces a
small problem. The decimal system uses ten numbers (0-9), but hex-
adecimal notation needs 16. Hex notation uses the first six letters of the
alphabet as the top six numbers. The letter A represents the number 10;
B has the value 11; C 12; D 13; E 14 and F 15. The following hexadec-
imal number can be converted as follows:
5DA9
16
3
= 5 * 16
+
13 * 16
+ 10 * 16
+ 9 * 16
= 5 * 4,096
+
13 * 256
+ 10 * 16
+ 9*1
= 20,480
+
3,328
+ 160
+ 9
= 23,977
Hexadecimal and octal numbers can be used in C exactly like decimal
numbers. Hex numbers use the format specification Ox (or Ox) to indi-
cate that they are base 16. For the octal system only a leading zero is
required. Some examples:
0X5DA9
OxFFFF
0612
0x5da9
0x123
0815
0X5da9
06543
One of the above combinations is wrong. Examine the numbers again
carefully. The error is hidden in the innocent number combination
0815. With the leading zero it should represent an octal number. There
is no digit with the value 8 in the octal system.
The response depends on the compiler. The compiler can issue a mes-
sage that a wrong number was entered, or accept it as a decimal number.
The Lattice C compiler converts the number from octal into decimal
notation. This produces something entirely different, namely 525 10
which is equal to 1015 g
The user would soon get tired of entering every number for conversion.
A good C implementation does that conversion for you.
To write a program to convert numbers from various bases into the dec-
imal system, the procedure must differ slightly. Nothing is simpler
than constructing a loop to save typing time. Starting with the last
position (9 in the last example), multiply it with the value of the posi-
tion. The value at the last position is then 9*1 = 9. The next
position has the value 16, and the variable containing this value with
the base (16). The next position is therefore 10*16 = 160.
81
9. PRINTF AND SCANF AMIGA C FOR BEGINNERS
All computed intermediate results are added in a separate sum. This is
the same path as the manual procedure with the exception that every
step again is divided into smaller steps. The user doesn't have to under-
stand how the calculation works, since you are trying to learn C and not
mathematics.
9.3.1 Conversion Program
Analyze the following listing on the basis of the explanations already
provided. If it isn't clear, a few print f functions inserted in the
program could print out the current value of one or more variables. This
makes the most important variables visible.
/* base-con. c 9.3.1 */
void main ()
{
long base, collect, value;
int index, help;
char test [100] ;
printf ("Please input Base of numbering system! \n") ;
scanf ("%ld", Sbase) ;
printf ("Input number for conversion in base %ld
system!\n", base) ;
scanf ("%80s", test);
collect =0;
value = 1;
index = strlen(test) - 1; /*New Function */
while) index >= 0)
{
help = test [index] ;
if (help >= 'a') /* lowercase letter */
help = help - 'a' + 10;
else
if (help >= 'A') /* uppercase letter */
help = help - 'A' +10;
else /* Probably a number */
help = help - ' ' ;
collect = collect + value * help;
index = index - 1;
value = value * base;
)
printf <"%s(%ld) = %ld(10)\n", test, base, collect);
)
The program uses the long data type a lot. This can also be noted in
the format specification %ld for the input and output of these variables.
The scanf function which reads a number as a string has something
new. After the percent sign appears an 80, followed by the format
specification %s for the string. This value between the percent sign and
82
Abacus 93 Octal and Hexadecimal
the format assignment tells the function the maximum number of
characters permitted. In this case the string cannot be longer than 80
characters (+ 1 end of line = 81). In reality this does not work out quite
that way. As a maximum only 80 characters are processed, but the user
can write several lines. Only the first 80 characters are used.
The indication of a maximum number of places is also permitted for
other data types (see the example in scanf ). A new function strlen
will be introduced next. It delivers the characters in a string. The con-
cluding zero byte is not included. The result is assigned with an equal
sign. The only parameter required by strlen is the string to be inves-
tigated. One of the examples already calculated the length of the string.
The strlen function is therefore not very large.
In the following while loop the string which was input is processed.
To avoid the use of the expression test [index] for every calcula-
tion, the character at that location is copied into the variable help. The
user should have noticed that help was defined as an integer variable.
Yet an attempt is made to store a character at that location. Computers
view characters as numbers. Every letter has a numeric code, just like a
number. The char variables are nothing more than small integer
memory areas which, depending on the compiler, accept a value
between -128 to 127, or from to 255. These peculiarities of calcu-
lating characters with numbers and their codes will be discussed later.
83
9. PRINTF AND SCANF AMIGA C FOR BEGINNERS
9.4 Character Codes
After the character was made available in help, it is tested to see
whether it was an upper or lowercase letter. These can be used as auxil-
iary numbers in a system whose base is larger than 10. In the hexadec-
imal system the letters A-F are used. When it has been determined what
type of character (uppercase, lowercase or number) is available, its
actual value is calculated. 9 is not equal to 9 here. Confused? You
remember how a character was assigned to the char variable:
character = ' 9 ' ;
The 9 is a character which represents the number nine. This character
also has a special ASCII character code. The ASCII code for the number
9 is the value 57. The assignment that follows gives the same result as
the example above:
character = 57;
Calculation with the variable requires the value 9 and not the stored
code 57. First subtract 48 from 57 (48 is the character code for zero (0)).
This is practical since all numbers are in sequential order with the
following codes.
Code Character
48
49 1
50 2
51 3
57 9
The letters of the alphabet also follow this order. The table starts with
A (code 65), B (code 66), etc. The lowercase letters are in a separate list
The first value there is 97 for the character a. Let's look at a program
section:
char
test
test
= 'B\-
test
= test
'A' + 10;
What is contained in the variable test after the execution of this
sequence? An equivalent part appears in the conversion program. The
right result is 11. In the last line, test contains the letter B with the
value 66. Subtracting A from this results in 1; plus 10 is 11. That is
the value that the letter B represents in the hexadecimal system.
84
Abacus 9.4 Character Codes
The following line converts an uppercase letter into a lowercase letter:
test = test - 'A' + 'a';
That is much more readable than:
test = test - 65 + 97;
or
test = test + 32;
The codes are nearly identical on almost all computers thanks to the
ASCII standard. ASCII assigns a specific code to each character.
To obtain an overview of the ASCII codes, the program below displays
every code and its character (32-127, 160-255). The codes 0-31 and 128-
159 were left out because they either have special functions (e.g., 13 is
equal to \n) or do not produce anything on the screen.
/* ASCII. c 9.4*/
main ( )
<
int i;
print f("\n\n") ;
for(i = 32; i <=127; i = i + 1)
printf ("\t%-3d %c", i, i) ;
for(i = 160; i <= 255; i = i .- 1)
printf C"%-3d %c \t", i, i) ;
printf ("\n");
These are all of the characters that can be printed with the printf
function.
9.4.1 About the Backslash
Output using a character code displays a character which cannot be
accessed with the keyboard or with the backslash. The backslash must
precede the code. The compiler replaces the combination of backslash
and the individual digits of die code with a single character. One hitch —
the number must be entered in octal notation instead of decimal nota-
tion. The following command displays the ± character (character code
177):
printf ("\261") ;
The number 177 decimal corresponds to 261 octal. The conversion can
be avoided using a format specification as shown below:
85
9. PRINTF ANDSCANF AMIGA C FOR BEGINNERS
printf ("%c", 177);
The character is not used directly in the string, but goes directly to the
printf function in the form of a character code, with the %c.
printf ("The result is \2611.\n");
printf ("The result is %cl.\n", 177);
The control character %c permits the output of a single character by
indicating the character code, even if an integer value was passed.
9.4.2 Going the Other Direction
The following program converts decimal numbers into octal numbers.
It is almost the reverse of the previous conversion program which con-
verted numbers into the decimal system.
/* dec-conv.c 9.4.2 */
void main ()
(
long base, test, help, rest;
int index;
char result [260];
printf ("Please input number Base!\n");
scanf("%ld", sbase) ;
printf ("Input number in decimal system!");
scanf ("%ld", Stest);
index = 0;
for (rest = test; rest > 0; rest = rest / base)
{
help = rest % base; /* Remainder of Division */
if (help > 9) /* Letter to substitute */
result [index] = help + *A' - 10;
else
result [index] = help + ' 0';
index = index + 1;
}
printf <"%ld(10) = ", test);
index = index - 1; /* last entry is still unused */
while (index >= 0)
{
printf ("%c", result [index]);
index = index - 1;
}
printf ("(%ld)\n", base);
)
86
10.
The Preprocessor
Abacus 10. The Preprocessor
10. The Preprocessor
The preprocessor is a part of the compiler program which first processes
the source code. It accepts source code text as written. There are some
special directives which force the preprocessor to make changes in the
program source code text. After the preprocessor has done its work, the
part of the compiler responsible for the translation uses this "processed"
version of the source code text. This version can appear quite different
from the listing.
To differentiate the preprocessor directives from other C statements and
functions, there are two important guidelines:
1 .) All directives begin with the # character
2.) All directives begin in the first column
10.1 #define
Let's first consider the most important and most often used preprocessor
directive: #def ine. #def ine replaces a certain character string with
another string. The preprocessor exchanges the two text strings. Let's
think about what the text replacement could be used for.
Assume that a constant is used during calculations. For example during
the calculation of a sales tax, a certain percentage (4% perhaps) appears
regularly. If this percentage is used 10 to 20 times in a program and the
sales tax percentage changes, a change in the program can become diffi-
cult. It can also lead to errors. Perhaps a wrong value would be returned
if the number 4 appeared elsewhere in the program. An entry can be
missed during the changes. It is simpler to use the #def ine directive.
An application would appear as follows:
#define TAX 4
Up to this line the text TAX can be used which is then replaced by the
preprocessor with the text 4. Also the following line could be used:
print f("TAX-rate %d", TAX);
The preprocessor passes to the compiler the following substitute line:
print f("TAX-r ate %d", 4);
89
10. The Preprocessor Amiga C for Beginners
Nothing has changed within the parentheses. This is good since it
would be impossible to output a string such as tax on the screen.
Nothing inside the quotation marks can be touched by the preprocessor.
Defines are always used in a large program. The following program
explains the usage of #def ines. What the program produces can be
seen readily in the listing:
/* define. c 10 */
#define BEGIN 1
#define END 100
#define STEPS 2
void main ( )
{
int i;
printf ("\n") ;
for(i = BEGIN; i <= END; i = i + STEPS)
printf ("%5d", i) ;
for(i = END; i >= BEGIN; i = i - STEPS)
printf ("%5d", i) ;
printf ("\n");
Even in a small program the use of #def ine directives can enhance
the readability of the program. An example is marking the end of a
string with a null byte. This null byte is also called end of string. With
the abbreviation EOS, it's an often used #def ine. The definition
appears as follows:
#define EOS <\0'
That is more correct than simply indicating a 0. The entries of a string
are considered individual characters. It is therefore good C style to use
data type assignments. The single quote mark informs the compiler that
a single character is used. The backslash followed by the octal value
indicates the character code (see Section 9.3).
The number zero in the octal system, the decimal and other number
systems is always zero. A conversion in this case isn't difficult. Using
the character with the code zero, or the code directly (zero) in the assign-
ment is of no consequence. In future programs which use strings, the
definition of EOS should appear in one of the first lines.
If the reader thinks that the subject of #def ine is now finished, he is
wrong. The many capabilities which are provided with the #def ine
directive, will be discussed in more detail in a separate chapter.
90
Abacus 10.2 #include
10.2 #include
Another important preprocessor directive is # include. A file can be
combined with the source file during compilation with this directive.
This is similar to appending a file to the current file (<Eso<IF> from
ed) and then saving the appended file. The compiler does not
differentiate where the definitions originated, because for the compiler
only one file exists. This preprocessor directive is ideally suited to
include multiple #def ine directives into the program. Assume that
the following #de fines were stored in a file with the name
def_new.h:
#define EOS '\0'
♦define MAXLEN 81
♦define EOF -1
If you have a source code text that uses these #def ine directives, you
don't have to re-enter them. All you have to do is tinclude the file
def_new.h:
♦include "def_new.h"
The file extension of .H stands for Header file. This ensures that all
#def ine directives are available throughout the listing. It is not a
requirement, but should be done anyway. Although this preprocessor
directive can appear at any place in a file, it is better to include it at the
head of the source code.
The filename is written between quotation marks. In this case, the
compiler searches in the directory where the source code is located. You
can also enter the include file within greater than and less than
characters:
♦include <def_new.h>
stdio.h The compiler assumes that the file is now located in a subdirectory in
which all .h files can be found. The path to this subdirectory passes to
the compiler during the start. There is a series of these files which are
waiting to be used. One of the most popular of these files can be found
under the name stdio.h. This stands for STanDard Input Output
Header file. In Lattice C, it is in the include directory. This file can
be examined using the ed editor.
91
11.
Abbreviations
Abacus 11. Abbreviations
1 1 . Abbreviations
We said earlier that C is an ideal language for lazy people who don't
like to type. This is still true, since C lets you compress many
functions into smaller packages using abbreviations. This chapter
describes the art of abbreviating code in C.
C abbreviations help save typing time. Let's start with the simplest
abbreviations — those used in arithmetic operations. The equation below
may look fairly familiar to you. Believe it or not, this can be converted
to a shortened form of the same equation:
number = number * 4;
What could be saved here? The variable number appears twice. This
doesn't have to be so. The C language allows you to abbreviate the
equation to the point where you only need to use the variable number
once instead of twice:
number *= 4 ;
Every time you use the same variable during calculation and for storing
the result of the equation, you can use this short form instead. The
multiplier gets moved to the left side of the equal sign. The multiple of
the variable number remains to the right of the equal sign.
The above abbreviation becomes most effective when using long vari-
able names. In addition, it helps decrease the number of typing errors
(the less you type, the fewer mistakes you make). For example, look at
the following abbreviation:
the_user_input [index] += ' 0';
The above abbreviation corresponds to:
the_user_input [index] = the_user_input [index] + '0';
Another advantage is the speed difference between the long version of
the code and the abbreviated version of the code. The execution speed of
each compiled code is different; the abbreviated version executes in less
time than the original. The compiler knows what values are used and
where to store the result. This can save a lot of unnecessary calculation
time.
95
11. Abbreviations Amiga C for Beginners
Implementing operator abbreviations is fairly easy to do. All arithmetic
operators can be changed into abbreviated form as seen in the following
list:
/=
%=
etc.
Consider the following expression. Can you see any possibilities for
abbreviating the code?
value = value * (5 + number) ;
The line is already written in such a way that the operator to be abbre-
viated becomes immediately obvious. It is the multiplication operator.
So, if you change the equation into abbreviated form, the source code
looks like this:
value *= (5 + number) ;
Since usually the right side of the equal side is calculated first, no
parentheses are required. Therefore, the final version of the short equa-
tion looks like this:
value *= 5 + number;
Now for the same thing in reverse. The operator and the named variable
can be attached to the terms, using parentheses. The following equation
also has potential for becoming an abbreviated version:
var *= numberl - number2;
corresponds to:
var = (numberl - number2) * var;
96
Abacus 11.1 Increment and Decrement
11.1 Increment and Decrement
Shorthand notation can be carried a step beyond arithmetic operators.
The operators ++ and — increment and decrement a variable's contents
by one. The ++ operator increments the specified variable by one, and
is therefore called the increment operator. The — operator (called the
decrement operator) acts in the opposite manner and decrements
(decreases) the specified variable by one. These operators appear as
follows:
main ( )
{
int i;
i = 1;
while (i++ < 100)
printf ("%d ", i) ;
This short program is deceptive. Up to the while loop everything is
clear. The i variable contains the value 0. Now comes the expression:
i++ < 100
First the computer sees if i is less than 100. Then it increments the
value of i by 1, regardless of the results of the test. This corresponds
to the following if /else/while:
if<i < 100)
condition = 1;
else
condition = 0;
i = i + 1;
while (condition)
Here all four listed directives are executed within the parentheses. That
makes the increment operator very powerful.
It gets better. The increment and decrement operators can be placed
before or after the variable, to serve different purposes. The location is
important, as you'll see. A simple example will illustrate:
i = j++;
97
11. Abbreviations Amiga C for Beginners
Assuming that j contains the value 3, i also contains 3. Then the
value of j is incremented by one to 4. In contrast, the next line places
the operator on the other side of the variable:
i - ++j;
With the same assumptions, the content of j is incremented to 4 and
then the variable i is assigned that value. Both variables now contain
4.
Remember, if you precede a variable with an increment or decrement
operator, the content of the variable changes before it is used for addi-
tional tests. If the operator follows the variable, first the current value
is used and then the variable is incremented or decremented. It is impor-
tant to remember this small but decisive difference. Examine the output
of the two programs on the screen. The first number which appears
there is two. That is clear since the starting value of i was one which
was already incremented inside the loop head with while. For this
reason, the i at the time the print f occurred already had the content
2.
These operators help to write fast and compact programs. They are even
more efficient than the abbreviations using the equal signs.
98
Abacus
11.2 Initialization, Definition, Declaration
11.2 Initialization, Definition,
Declaration
Initialization These three concepts are very important for the C programmer and
should not be confused. Let's begin with initialization. It describes the
first assignment of a value to a variable. After this point you know
what the variable contains. Before the variable can be initialized, it
must be defined or declared. Definition takes forms similar to the fol-
lowing:
int index;
char string [80];
When the compiler reaches this point, it knows the variables and sets
aside the necessary memory area for them. An integer value generally
requires two bytes. The variable string requires 80 bytes since every
char element requires one byte. Functions can also be defined. Up to
now only the definition of main was mentioned. If you declare a
function or variable, this only tells the program that such a variable or
function was defined somewhere. For this reason no memory is allo-
cated.
Definition Here's a tip for saving lines of code. Variables can be initialized during
definition. That saves one program line:
int index = 0;
Any expression can be assigned to the newly defined variable. The
string length which was determined with the strlen function can be
used during initialization as follows:
int end = strlen (string) - 1;
Of course st ring must have been previously defined.
Some coding can seem exaggerated, but there is no limit to your imag-
ination.
long middle = 4* ( (strlen (stringl)+l) /2+1) -strlen (string2) /3;
Declaration If you write a large program stored in several modules (files), a variable
used by all modules only requires a single memory allocation. The
definition is in one file and all the other files only contain the corre-
sponding declaration. Declaration is made with the C word extern.
The compiler knows that the memory was reserved externally through
another file. Otherwise the linker stops unking. Example:
99
11. Abbreviations Amiga C for Beginners
extern char pass_word[80] ;
extern int error_nr;
The example above shows that the data type must also be specified.
This provides all the information necessary to the compiler about the
variable. The function declaration is similar.
extern long atolO;
If you define the function in the same file, the extern can be omitted.
The declaration is still required since the compiler knows the function
names and their data types only at the end of the file.
100
Abacus 11.3 Multiple Assignments and Directive Value in c
11.3 Multiple Assignments and
Directive Value in C
Source code can also be abbreviated by using multiple assignments. If
several variables are to be assigned the same value, individual
assignments were previously required for every variable. The same
value was given for each:
begin = 0;
sum = 0;
However, the following line performs the same function:
begin = sum = 0;
The assignment is from right to left. First is assigned to sum and
then begin gets the content of sum which is 0. A term with more
simultaneous assignments could be enclosed in parentheses, which
would make the sequence more readable. Here's one version:
a=b=c=d=2;
This version shows added parentheses for readability:
a = <b = (c = <d = 2)));
Individually expressed, the two above lines correspond to the expres-
sion:
d = 2;
c = d;
b = c;
a = b;
Multiple assignment is possible since every expression has a value (the
result of the last operation performed). For example, the value of
(d=2)2,of (index = strlen (string) ) strlen (string) .
Except for large initializations of variables, the value of an expression
can be used almost everywhere. It also shows who knows C well. The
shorter formulation will identify the professional.
Examples can show this better. Here are some more values for expres-
sions:
(2)
2
(a)
a
(a *=3)
a*3
(a=(b=(a+2)-3))
a-1
101
11. Abbreviations Amiga C for Beginners
The last example must be dissected into its components to reach the
same result
(a=(b=(a+2)-3)))
(a=(b=a-l ))
(a=(a-l ))
(a-1)
Of course the advantages of the multiple assignment can be used during
the definition and initialization. The following line is permissible:
int start = value = 0;
The variable value must be predefined and initialized (very important)
which is the case here.
102
12.
Functions
Abacus
12. Functions
12. Functions
You read in the introduction that a C program sometimes consists of
many different functions. Up to now only one has been defined (the
main function). It's time to start writing programs which contain
several functions developed by you.
Function First, the formal structure of a function definition. You must specify
structure the function name, preceded by the data type returned by the function.
The name must correspond to the usual rules for variable names.
Parentheses containing the arguments follow the name. If no such
values exist (e.g., the main function) none can be indicated. If such
arguments are expected, these variables must be declared. The values are
important since most functions get information from other functions
which are then processed. Then follow the executable commands, also
enclosed in parentheses.
Let's look again at a simple version of the main function:
main ()
{
The first item to be encountered according to specifications is the data
type which the function returns. Since the main function doesn't return
any values to the calling program, the data type is omitted. The word
void usually appears preceding a function that returns nothing.
Next the function name (main) is specified, followed by a pair of
parentheses. Since no values are passed to the main program, no data
appears between the parentheses. The variable declaration is also
omitted, since nothing is passed. Then follow the other executable
instructions within the braces, which up to now was the complete
executable program.
105
12. Functions Amiga C for Beginners
12.1 Functions with Arguments
The next step is to dissect the program into individual tasks. You can
write a short function for every partial task. For example, a function to
compute the square of a value requires no great mathematical training:
double square (x)
float x;
{
double q_n umber;
printf("The square of %f\n is ", x) ;
q_number = x * x;
return q_number;
}
The square The above routine defines a function named square which in turn
function returns a double value to the calling program. As a parameter to be
passed, a float value called x is required. At the end of the routine a
new C word appears, the return keyword. It delivers the desired result
of the specified data type to the caller and also ends the function.
It is important that no semicolon follows the function name. There
must be a semicolon after each parameter declaration. This differentiates
a function definition (without semicolon) from a function call (with
semicolon). The following line identifies that a function named square
is to be used by the main program:
double square!) ;
main ()
{
float value = 3.0;
double result;
result = square (value)
}
The names of the parameters passed by the calling function need not be
identical to those of the called function. However the data types must be
the same. Notice the line in which the square function is declared as
a function which returns a double value.
106
Abacus 12.1 Functions with Arguments
The declaration can be omitted if integer values are returned. The same
is true for the definition of a function. If the function returns integer
values, a data type need not precede the function name. This is only
possible with data type int. All other types must be declared and
supplied with the proper data type during the definition. If one of these
data types is contradictory (perhaps because the declaration forgot a
double function) the resulting values will be wrong. While the C
language permits much freedom to the programmer, but this can cause
much trouble.
107
12. Functions Amiga C for Beginners
12.2 Functions without Return
Values
Some functions return no values. These functions can be declared as
void, if the compiler has implemented this C keyword. This can
improve the speed somewhat since the parameters need not be prepared
for the calling function. Even that may be omitted, which is the reason
why some C compilers don't define the void type.
/* key.c 12.2 */
void key (string) /* Without Return value: void */
char string [80];
{
int i;
for(i = 0; string [i] > 0; i++)
printf("%c", string[i] + 1); /* From -A' make -B- */
}
void main ( )
{
char text [81] ;
void key () ;
printf ("\n\nPlease input some text!\n");
scanf ("%80s", text);
key (text) ;
printf ("\nin the original it was %s\n", text);
)
The new defined functions are called exactly like the routines from the
libraries. In this example the main function stands at the end of the
file. The routine named key is declared as a function which returns
nothing, or void. That is important since the definitions would contra-
dict themselves during usage in main. If the function had not been
declared, the compiler would assume that it should return int objects.
It returns nothing.
108
Abacus 123 Other Functions
12.3 Other Functions
Another function which does not return a result is strcpy. This rou-
tine copies strings, and performs general string handling. Even though
it's included in every compiler's library file, it is interesting to see how
it can be programmed.
12.3.1 strcpy-Version 1
This copies one string to another. Unlike the previous example, you
don't know how many entries are in each string. This can be omitted. It
is enough for the compiler to know that it will get a string.
In the routine itself, a counter tests all entries. They are copied until the
routine reaches the EOS character (the end character must also be trans-
mitted).
#define EOS '\0'
strcpy (to, from)
char to [ ] , fromt ] ;
{
int i = 0;
while((to[i] = from[i]) != EOS)
i++;
)
The function is indifferent to the memory requirements of the array,
since it doesn't have to set aside any memory. The strcpy function
works directly with the strings passed to it from the calling function.
The strings may be of different lengths.
What do you think of the termination conditions in the while loop?
The position of the parentheses makes the processing clear. First is the
assignment of f rom[i] to to [i] . The expression in parentheses
also has the value f r om [ i ] , and also the character which was copied.
This is now compared with the end code character. If you copy the EOS,
the condition is no longer true and the loop terminates. Otherwise it
increments the current counter and remains in the loop.
109
12. Functions Amiga C for Beginners
The actual loop body has only a peripheral role. The main action occurs
in the ending conditions. Experiment with this function. Notice that the
string into which the copy is stored appears first. Here is a complete
example program:
/* copysrt.c 12.3.1 */
#define EOS '\0'
#define MAXLEN 81
strcpy(to,from)
char .to [ ] , from [ ] ;
{
int i = 0;
while((to[i] = fromfi]) != EOS)
i++;
)
void main ()
{
char si [MAXLEN], s2 [MAXLEN], s3 [MAXLEN]; r
printf("Your name, please\n") ;
scanf ("%40s", si);
strcpy(s3, si);
strcpy(s2, "TEXT IN s2") ;
printf ("Therefore %s, in s2 is \"%s\".", si ,s2);
printff" I hope %s, that everything is clear!\n", s3) ;
}
The strcpy function can be used to initialize strings since the
following expression is not permitted in C.
Wrong:
main ()
{
char text [20] = "This_is_text ! ";
}
Right:
main ()
{
char text [20] ;
strcpy(text, "This_is_text !") ;
)
This copies the complete string into the variable text.
110
Abacus 123 Other Functions
12.3.2 strlen
You used the strlen function earlier in this book. It is simple to
write and return a value. The passed length of the string is a whole
number and should be an integer value.
strlen (string)
char string [];
<
int i = 0;
while (string [i])
i++;
return (i) ;
)
A nice short function! The expression string [i] is always the
content of this element. This means that the expression is only (false)
when the end character \0 (EOS) has been reached. The counter which
corresponds to the length of the string passes to the calling function as
an integer value through a return directive. This function doesn't
have to be declared in the calling function because it returns an int
value.
If the return directive passes data, it must be assured that the value
has the proper data type. If the function definition states that the routine
returns a char element, there should be a variable or constant of the
char type. Some compilers will not tolerate such mistakes and will
issue an error message. Others are indifferent and convert the result into
the data type indicated in the definition. It's better to do it right in the
first place.
Ill
Abacus 13. Arrays
1 3 . Arrays
Up to now strings have been used as if they were a special data type. A
string is actually multiple char entries. A string of similar objects is
called an array. Arrays can also be made using int or float data
types as well as char types. Any elementary data type can be stored in
an array. Several similar variables can be accessed through a single
identifier. A single element is accessed by using a subscript called the
index (counter). The definition of a long array differs little from string
definition:
long value [20] ;
This line reserves 20 elements of type long for the variable value.
To indicate the end of a string, the last entry contains the value 0, i.e.,
assigns the escape sequence \0. For this reason, the definition of a
string (character array) requires one element more than needed for the
actual string. No such requirements exist for other array types: Only as
many entries are defined as required by the data. A value assignment of
one element is possible only by providing the index. For example:
value [01 = 4711;
value [1] = 707;
value [2] = 31415;
The index value of the first element always starts with 0. Using this
method, you can create a string one character at a time:
char string [80];
string [0] = • 0';
string [1] = 'K';
string [2] = ' \0';
This tedium can be avoided by using the strcpy function. The
assignment sequence above would store the string value OK into the
variable st ring, and is terminated with the usual end code \ .
Again the difference between a single character and a string of characters
should be emphasized. The difference between "K M and 'K' is that "K" is
a string, while 'K' is a character. If a letter is enclosed in "quotation
marks" like a character string, it is a string. It is also terminated with a
\ so that "K" consists of two characters, the K and \ . However, 'K'
is only a single character. This condition must always be observed since
all operating system routines assume that the string terminates with
\0. The last element that may be accessed has an index value of 79,
according to the declaration above of string [80] (counting starts
with 0).
115
13. Arrays Amiga C for Beginners
13.1 Multi-dimensional Arrays
Up to now we've been using one-dimensional arrays, i.e., variables
which use a single subscript. Multi-dimensional arrays have elements
like a one-dimensional array. However, multi-dimensional arrays have
multiple elements. For example, if you were designing a chess game in
C, you'd might use an 8 x 8 array for chess board data:
int field[8] [8];
Both elements are of course between and 7. You need two subscripts
to access a single field:
print f ("Content of Line 2 Column 4 %d\n", f ield[l] [3] ;
You can define an array with up to five sets of elements:
long content[4] [5] [6] [7] [8];
Please observe that arrays can quickly occupy large amounts of mem-
ory. The array above would require 4*5*6*7*8*4 (size of a
single long element) bytes (26,880 bytes or 26.25K).
Data can only be stored sequentially in memory. The user must get
away from the notion that a two-dimensional array is located in two
tables which are one in front of the other. How would a five-dimen-
sional array be stored? Since all elements are stored in a long series
(one-dimensional) there is a rule which must be followed. The first
index changes only when all elements which belong to its group are
stored. During the second index that occurs more frequently and the last
index changes with every element. This concept is easier to understand
in a listing which shows the position of the entries in memory.
Assuming a definition of int pos [ 4 ] [ 3 ] ;, entries in memory are:
[0] [0]
[0] [1]
[0] [2]
[1] [0]
[1] [1]
[1] [2]
[2] [0]
[3] [1]
[3] [2]
116
Abacus
13.1 Multi-dimensional Arrays
To conclude this chapter we want to present a program which operates
with arrays, and touches on many topics previously discussed. The
program tests a series of numbers, passes them to a routine which adds
them and receives a sum back. Then it makes statistical evaluations to
determine if it's worth storing the values. An array stores the data
entered. There are also some tricks which should be examined closely.
/* array. c 13 */
tdefine FALSE
#define TRUE 1
tdefine MAXENTRY 20
long total 0; /* Declaration of the function */
void mainO
{
int i, number, end = FALSE;
long sum, data [MAXENTRY] ;
for(i - 0; i <MAXENTRY &S lend; i++)
{
printf ("Enter %d. value: ", i+1);
scanf ("%61d", Sdata(i]); /* 6 digits limit */
if <!data[i])
end = TRUE;
}
number = i - end; /* If last data 0, than one less */
sum = total (data, number);
printf ("The Sum of all %d values is %ld\n", number, sum);
printf ("Deviation from Average %.91f:\n", (double) sum
/ number) ;
for(i=0; data[i] > 0; i++)
printf ("Value %d: %5.91f%%\n", i+1,
data [i] * 100.0 / ( (double) sum / number ) - 100.0);
}
long total (array, cnt)
long array[);
int cnt ;
{
long sum = 0;
while (cnt — ) /* short and precise */
sum += array [cnt];
return sum;
)
Lattice
The library for mathematical functions and floating point numbers must
be linked with the standard library. Example:
lc -Lm array
117
13. Arrays Amiga C for Beginners
Aztec If you work with the Aztec compiler, the library for mathematical func-
tions and floating point numbers must be linked with the standard
library clib. Example:
cc +L array.c
In array. o -lm -lc
First some information on the program. To make it more secure, only
20 entries are permitted. The #def ine MAXENTRY allows you to
adapt the program to larger input.
The declaration of the add function is important. Since this function
uses long values, the compiler must be told this. The declaration can
be performed within the main function.
The && operator ends the for loop which connects two tests logically
with an and. If not all entries are occupied, and the variable end is
unequal to 0, the loop executes.
Negation The negation operator converts end into the logical opposite. At the
beginning the variable contains the value so that the expression
becomes ! end 1. The reverse occurs when end is set to 1 and the
negation ! end is used to leave the loop. This happens when the user
enters the number 0, indicating the end of the input.
The first entry in the array requires the index 0. Since the count usually
starts at 1, a 1 is added to the current index during text output. In the
formulation of the scanf function, the following is most important:
Sentry [i]
If another array was input, no & character appears. That was the big
exception. Since entry [i] and not entry was written, this is not
an array, but a perfectly normal long variable. During the scanf
routine it is equipped with the & like all elementary data types. The fact
that this variable is in a long string of similar elements doesn't concern
the scanf function.
The following if test also merits closer examination. This is a typical
case of C abbreviation. The test should pass the value 1 to the end
variable if the current input was a 0. The following shows this:
if (entry [i] == 0)
If entry [i ] contains a zero, this expression is also zero. With the
help of the negation operator a true result is obtained. Especially for the
test == or ! = 0, the abbreviations are often placed in the location
where you would expect to find an explicit value. It doesn't complicate
the matter, but the user must know what is hidden there.
118
Abacus 13.1 Multi-dimensional Arrays
When the loop finishes, either because 20 entries had been made, or the
last entry was 0, the total number of the stored data is calculated. The
add function gets the necessary data (the array with the input and the
number of values to be added). This routine returns the sum. With this
information the deviation of each entry from the average can be calcu-
lated. If the task of the program was only to add a series of numbers, no
arrays would be needed but all entries could be summed after their entry.
119
14.
More about Loops
Abacus 14. More about Loops
14. More about Loops
This chapter takes you through a few of the fine points of using loops
in C programming language. You've already seen for loops and
while loops.
It also demonstrates some refinements to the for loop; statements
which help control loop programming (break and continue); and a
function for switching around within a loop (switch).
14.1 More About the for Loop
We described the for loop earlier in this book. Now we'll look at the
limitations and flexibility of the for loop.
Individual components of the for loop are separated by semicolons.
Several statements can be placed within the initialization and the
increment expressions. They use commas as separators, instead of
semicolons. This is how the for loop can be used:
for (sum = 0, i = 1; i <= 20; i++0
sum += i;
or also
for(i = 1, j = 0; i < 10; i += 2, j+=3)
This is the usual construction for a for loop. Since C permits other
variations, this example is presented:
for(printf ("Now we start!"); ; printf ("Bang\n") , i++)
if ( (c - input ()) == 'e')
break;
The text "Now we start!" appears at the beginning of the loop. A
test is then made to determine if the condition located between the
semicolons is true. This is always true since nothing is entered there.
You may recall that, under every condition, a null value is always
considered a false condition. Everything else is considered logically true.
The condition in the loop is always true. The only way to stop the
program is to press the <E> key, provided there is an input function.
123
14. More about Loops Amiga C for Beginners
14.2 break
If the test for if is true, the break statement is carried out. The
break statement ends the currently executing loop immediately and
forces the program to continue with the statement that follows the loop
that just ended. The break statement is the only way to break free of a
loop at any time.
Look at the program in the preceding section. The increment proceeds
in an unusual fashion. A print f call can be found there. This
print f executes at the end of each loop execution (notice that not
much remains of the original construction). An endless loop, which
doesn't have an initialization, a test or incrementation, would appear as
follows:
for ( ; ; )
{
}
A for loop can always be replaced with a while loop, and vice versa.
The general format is:
for(terml; term2;term3)
{
other directives
}
or
terml;
while (term2)
{
other directives
term3;
)
124
Abacus 143 continue
14.3 continue
The continue statement does the opposite of the break statement
Instead of leaving the loop immediately, the program jumps to the next
directive in line for execution after the last directive within the loop is
processed. For the three types of loops this is:
1 . The body of the whi le loop (within the parentheses)
2. The incrementation of the for loop, therefore f or (...; ... ;
continue)
3. The directive after do, in do...while
Example: calculate (field)
double field[ 1 ;
{
int i;
for(i=0; i<number; i=i+l)
{
if(field[i] == 0.0)
continue;
continue here!
}
)
If an entry within field should have a zero value, the continue
directive then executes. The program continues at location i=i+l as if
the loop block had been terminated.
125
14. More about Loops
Amiga C for Beginners
14.4 The switch Directive
This directive allows you to handle several similar comparisons. This is
presented in the following short program:
/* switch. c 15.4^*/
void main ( )
{
int number;
printf ("Please input a number ! \n") ;
while (1)
{
scanf("%d", « number ) ;
switch (number)
{
case 9:
printf ("Larger than 8\n"),
case 8:
printf ("Larger than 7\n");
case 7:
printf ("Larger than 6\n") ;
case 6:
printf ("Larger than 5\n") ;
case 5:
printf ("Larger than 4\n");
case 4 :
printf ("Larger than 3\n") ;
case 3:
printf ("Larger than 2\n") ;
case 2:
printf ("Larger than l\n");
case 1:
printf ("Larger than 0\n r
case 0:
printf ("Number !\n") ;
break ;
default :
printf ("Single number only!\n");
}
if (number == 4711)
break; /*Leave endless loop */
>
The switch statement is given the value to be tested (switch(c)).
Within the block of statements, this value is compared with the values
behind the keyword case. This value, which must be followed by a
colon, is then followed by the statements to be executed. If the
126
Abacus 14.4 The switch Directive
comparison is positive, if all values agree, the statements following
case are executed. If the comparisons are negative, the next
comparison is tested and all statements to the next case are skipped.
The C keyword default permits execution of statements if no
comparisons were successful. In comparison with the if test,
default corresponds to the else branch of the if construction. If a
test is positive, all of the following commands are executed. A stop
doesn't occur before the next case. In order to stop this process, a
break statement is required for each case statement.
If the character passed for the test is for example a 5, all directives (also
those behind case 4, 3, etc.) are executed up to the next break
directive. This causes the direct termination of a loop, or in this case
the switch directive.
Even if several directives are executed behind a case, parentheses are
not required. With switch all elementary data types except for float-
ing point numbers can be compared.
127
15.
Pointers and
Addresses
Abacus 15. Pointers and Addresses
15. Pointers and Addresses
This chapter discusses the most important components of the C
language. Pointers are loved by some and hated by others. In a discus-
sion of the advantages and disadvantages of C, inevitably the word
pointer will be mentioned. It is possible to write fast and short routines
with pointers, but some programmers who have never worked with
pointers are completely confused by them.
15.1 Addresses
Let's start slowly. The pointer concept has close connections to the
address concept. During the call of the scanf function, the & (address)
operator had to be placed in front of most variables. This construction
allows the determination of a variable's memory address. All data,
whether floating point numbers, integers or characters, are stored
somewhere in the computer. The position where variable data can be
stored is determined by a number (the address). In general, an address can
be compared with the house number on a long street. This number is
obtained from the variable which is preceded by the & character.
Assume that the variable a was defined and is stored starting at address
100. The expression &a would return the value 100. Why are addresses
required, if you can work without them?
The user who experiments with his own functions, may soon find that
the called function should pass more than one returned value to the
calling function. It is also difficult to change the content of a variable
defined in another function. Consider the following section from a
program:
{
int number = 6;
change (number) ;
}
change (newnum)
int newnum;
<
newnum =5;
)
131
IS. Pointers and Addresses Amiga C for Beginners
The change function receives a copy of the content of number only
during the call. If this function changes the value of the variable
newnum, the original, which is in the calling function, remains
unchanged. This was already used in a program. Examine the program
which calculates the sum of individual array entries. The variable amt
decrements to zero, while the variable number is used later for
calculation of the average.
Now we have a way to pass the address of the variable. The calling
function can access them directly and the function does not contain a
copy of the variables. In what data type should this address be stored?
132
Abacus 15-2 Pointers
15.2 Pointers
Principally the address could be stored in an int or long variable.
This depends on the size of the int type and the processor, as well as
how many bits are required for an address. The Amiga requires 32 bits, a
long value. Not all compilers offer this capability. C may be flexible,
but some compilers are better than others. Storing addresses in long
variables is not good programming because the programs may not be
portable to other computers. It is better and safer to use the data type
adapted for it, the pointer. A pointer is marked by the special character
"*". Since the data type is indicated during the definition of a pointer,
the pointer is more than just a replacement for the long variable,
What function does the pointer serve? As mentioned, it should accept an
address. With this address it can access an object, here the content of a
variable. During the definition the pointer obtains additional
information about what data type is involved. It knows what values it
points to. For example:
char text [80] ;
char *pointer; /* Define pointer to char-elements */
text [6] = 'a 1 ;
pointer = Stext[6];
The first command defines a char array (string). The next line is the
definition of a pointer which is called pointer. An asterisk precedes
the pointer name, which labels it as a pointer. In addition (as in all
other variable definitions) the data type is indicated. In the next line, the
character a passes to the array element with the index 6 (7th entry).
Now the pointer appears, which gets the address of element 6 with the
address operator &. Since pointer now contains the address of this
element, it points to the character a. The pointer points to another
variable, text [ 6 ] . This is also called referencing, and the reversal of
this process is known as de-referencing.
Now access can occur to the letter through the initialized pointer. The
next directive could be:
if(*pointer == 'a')
printf (That's it!\n");
If the element in the memory location should be accessed, the pointer
variable must be preceded by the asterisk. The expression *pointer
is a synonym for text [ 6 ] (of course, only if *pointer points to
that position). Also the change of the content of this memory location
is possible through the pointer:
133
15. Pointers and Addresses Amiga C for Beginners
♦pointer = 'b';
After this directive 'b' passes to the location to which the pointer is
pointing instead of 'a'. Without using the array, its content was
changed.
15.2.1 The Exchange Function with Pointer
Now a routine which should change the value of the calling function.
The exchange function:
exchange (xp,yp)
int *xp, *yp;
{
in help = *xp;
*xp = *yp;
*yp ~ help;
}
This function expects two pointers to the int values passed as param-
eters. For the exchange the first value which points to xp is saved in
the integer variable help. Then the values are exchanged. The call of
the function must also be changed in comparison with the previous
calls since pointers to their addresses, not int values, are expected.
int value 1, value2;
value 1 = 3;
value2 = 5;
exchange (svaluel, Svalue2) ;
Perhaps now you can understand why, in a scanf the address operator
always had to be used. With this function, data are written into the
variable, which is only possible with pointers and addresses.
In arrays, especially in the frequently occurring strings, access to indi-
vidual elements can only occur with the index. The address for a single
entry must be obtained with & array [index] . For the first element
in this list the following must be constructed:
iarray [0]
In C the name of an array is nothing more than the memory address of
the first element so it can be abbreviated. For &array[0] can be
written array. Both return the address of the first element, not its
content. An array name already acts as a pointer which points to the
first element. Now it should be clear why during a call of scanf, the
name of the string did not have to include the address operator &. It is
already the address:
134
Abacus
15.2 Pointers
char string [81];
scanf ("%s", string) ;
It was not an exception, only a short version of & string [ ] .
15.2.2
strcpy-Version 2
String copying is an ideal application of pointers. Through the use of
pointers, the indices which had to be used during the first formulation
of strcpy, can be saved. The following construction with pointers
illustrates an example:
strcpy (to, from) /* Version 2*1
char *to, *from;
{
while <<*to = *from) != '\0')
(
to++;
from++;
Pointer In the strcpy routine above, the peculiarity of the pointer becomes
increments obvious. If die pointer increments by one, the pointer points to the
next element If it increments by two, it points to the element after the
next. In this strcpy version, a character is transmitted from from to
to until the transmitted value is equal to 0. At that point the expres-
sion (*to = *f rom) has the value 0. When this expression becomes
unequal to 0, the while loop terminates. The last transmitted character
is the just tested null byte which represents the end code of a string.
15.2.3
strcpy-Version 3
The previous routine would not be a C program if it couldn't be
shortened. A null test can usually be bypassed and the incrementing of
the pointer can be squeezed into the termination conditions. Therefore
the shorter version:
strcpy (to, from) /* Version 3*/
char *to, *from;
<
while) (*to++ = *from++)
)
135
15. Pointers and Addresses Amiga C for Beginners
This should be one of the shortest and fastest versions for copying
strings which could be made faster only with a special trick. More on
this later.
To write a program which transmits float values instead of char
values from one array to another, only one word must be changed in the
formulation above. That word is char. In its place the data type
float is used and immediately float values, which have a
completely different construction and require much more memory space
per element, can be copied. How is it possible?
With the definition:
float *to, *from;
the program is informed that the pointers from and to are pointing to
values of data type float. This data type generally requires 4 bytes per
entry. If such a pointer is incremented by one, for example af ter++,
it points to the following element. It is located four bytes from the
original element, but the compiler knows it through the definition of
the pointer. Through the incrementing of the pointer by 3, the address
would change by 12 bytes. In the data type double, which normally
uses 8 bytes, this can also be used. For each increment of the pointer,
the address is changed by 8 bytes. A pointer is a very nice feature.
How does the compiler process expressions such as string[4], when
these groups are related to each other? Since string is the name of
the array, which in C corresponds to the first entry (string[0]) ( the
compiler converts this expression into the equivalent *(string +4).
First the length of 4 elements is added to the address string. This
makes the current pointer point to the entry string[4]. Then access
to this element is accomplished through the asterisk. The parentheses
are required because the pointer "*" has higher precedence than the
addition (a table of precedences can be found in the Appendices). A
comparison between pointer and array can be made clear with the
following examples:
long value, data [10]; /* Defined like this */
Array the same with pointers
value = data[3]; value = *(data +3) ;
data [10] = value; *data = value;
data[7] += value; * (data + 7) += value;
136
Abacus 15-2 Pointers
As shown in the program above, other operators can be used in the
construction *pointer. For example the *af ter++ directive in
strcpy indicates that first the value, to which after points
(* after), is obtained and then the pointer should point to the next
field (++). Can you imagine what the following directives would do?
int i, *ip = Si;
i = 100;
— *ip;
After the definition of the variable i and the int pointer ip, which is
also initialized here, the variable i gets a value assigned. Trie number
100 is stored in it Now comes the big question, what does — *ip do?
First the number (100), to which ip points (*ip), is obtained. Then
this value is reduced by one, thus 100 becomes 99. This value is not
stored in variable i. The same result could have been obtained with the
much simpler expression — i.
137
15. Pointers and Addresses Amiga C for Beginners
15.3 Pointer without Storage
During the use of pointers, you should note that they represent only a
pointer to a certain data type. The memory locations for the individual
elements must be defined separately and the pointer pointed to them.
The initialization of the pointer prevents the system from giving wrong
answers or crashing. If a crash occurs when using pointers, even during
the test run of a program, first check where the pointers or the array
index are pointing.
A few occasional programs seem to contradict such demands:
main ()
{
char *text_ptr;
text_ptr = "All point to me!";
printf ("The text is >%s<\n",text_ptr) ;
}
Where in this program is the memory space for the string? The pointer
does nothing in this direction. It is stored somewhere in the program
text, just like in function calls (e.g., printf ("Hello\n") ;). Also
this string within the function must be stored somewhere.
Attention: If the text should be changed, for example with access through
text_ptr, the maximum length must be observed. In the string
above, this is only 28 characters, with one character representing the
end of the string \ 0. If 30 characters are written into this space anyway,
a system crash can be expected. It is possible that behind the string,
program code was stored which was overwritten. Should the computer
encounter such data which it cannot understand, it will go crazy.
The name of the array symbolizes the first element in the chain. Now
the question, what is the expression field[3] [2], if the following
definition has been issued?
int field[5] [5] [10];
Is it an element of this array? If so, which one, and if not, what is the
element? Examine the expression carefully. It only contains two
indices, but the definition contains three. It follows so that it cannot be
an extra element It can only be a pointer which points to the first (?)
element. The first element isn't f ield [ ] [ ] [ ] , but the first field
to which field [3] [2] points.
138
Abacus 153 Pointer without Storage
Is it clear now what wonderful changes can result from forgetting an
index? One element of the field becomes a pointer to a field in which
the missing index is replaced with [ ] . Therefore f ield [ 3 ] points
to field [ 3 ] [ ] [ ] . If something like this is possible, it can be
done with pointers. Later we will see some other tricks with pointers.
139
16.
Storage Classes
Abacus
16. Storage Classes
16. Storage Classes
This chapter discusses various groups of variables. These variables have
different lifespans during program execution. There are four storage
classes: auto (or local), global, register and static. Each
of these storage classes help your programs identify which C functions
recognize which variables, and determine how long the functions should
use these variables.
16.1
Auto
auto Even though the name is unfamiliar to you, you've been using the
variables auto (local) variables all along. The auto variables represent the
default storage class in C language.
These variables belong to the auto class because they are automati-
cally defined every time a function is called. On the function call, C
allocates memory space for the auto variables. The lifetime of an
auto variable is limited to the function in which the variable is
declared. After the function is abandoned through return, or the last
brace of this function is reached, the memory space allocated is released
and can be used for other assignments. These auto variables can only
be used in the function for which they were defined. The content of the
variable is lost and the name is not known to the rest of program.
143
16. Storage Classes Amiga C for Beginners
16.2 Static
static Unlike auto variables, static variables are retained until the end of
variables the program and are not deleted after leaving the function. They do not
have to be created again during a new call of the function. Leaving,
which means the termination of the executing function, should not be
confused with another function call within this function. Control may
briefly pass to another routine, but the calling routine remains active
(it's waiting for a result).
Here's an application of a static variable. The C word static
appears in front of a definition. For example:
function ()
{
static int counter = 1;
}
During the first call of the function, the variable is defined and initial-
ized with a starting value as in the example above. If the function is left
temporarily, a new variable isn't created during the new function call
because the variable still exists. Even its content remains and it does
not have to be initialized again. For example, a counter in this routine
could track how many times it had been called.
144
Abacus
163 External
16.3
External
extern The next storage class is the extern or global variable. These vari-
variable ables are defined outside the function and can be used by all functions.
A section of a program would appear as follows:
#define EOS '\0'
int error, dummy;
main ()
{ . . .
)
The variables which were defined can also be used by functions which
are not in the source file. The linker is given a number of files for link-
ing. These files contain functions which have already been compiled.
They may need global variables which must be assigned the right
values in their program. Such variables must be declared before using
them with the extern function, but they don't have to be defined:
extern int error;
This permits the use of the variable in a file in which error was not
defined.
Combinations, such as global static variables, are also permitted.
Through this definition all functions can access the global variable
within the source file, but the situation just described of accessing this
variable with a function from another file is prohibited. The variable is
only known to the source file. Functions which first come in contact
with the program through the linker, have no access to this variable.
145
16. Storage Classes Amiga C for Beginners
16.4 Register
register The last storage class is register. Those of you who have some
variable programming experience with assemblers know what this means. A
processor, the most important part of a computer, has various internal
memory locations. One such memory segment, which should not be
confused with the RAM of the computer, is called a register. The
number of registers which can be used depends on the type of processor
used. A 6502/10 used in the C64, or in the Atari 600/800/130, has
only three registers (2 registers and an accumulator). The MC68000
used in the Amiga, Atari ST and Macintosh has 17 registers. Each
68000 register is four times the size of a register in the 6502. For this
reason there are almost no compilers for 6502 computers which offer
the capability of register storage for variables. Of the 17 registers in the
computer, only three to five (depending on the compiler) are made avail-
able for storage. The remaining registers are required for internal use.
A variable defined as register must fit inside a register. A 68000
register is equal to 32 bits (four bytes), which only permits integer
numbers. Even if the float value could occupy only 4 bytes, it
cannot be stored in a register. Valid data types are:
int
char
short
unsigned
long
combinations
of the above
pointers
Pointers are possible since they only represent the address of an object
In the Amiga they only occupy four bytes.
There are other restrictions. The defined variable can only be an auto
variable since it occupies a register of the central processor. They are
rarely used and can be occupied only for a short period of time. After
leaving the function in which it was defined, the register is released
again for other purposes.
The register variable has a speed advantage over other variables.
The program can only fully utilize this speed when these variables are
used during many loop repetitions or calculations. The variable does not
have to be loaded from memory into a register for every use, since it is
already present.
146
ABACUS 1<- 4 REGISTER
16.4.1 Fast strcpy Routine
Before we present the first example, we must discuss another
limitation. It isn't possible to obtain the address of a register
variable with an & operator, because a register doesn't have an address. It
is not located in RAM.
strcpy (to, from) /* last version */
register char *to, *from;
{
while (*to++ = *from++)
)
This definition of the char pointer as register should receive the
maximum speed that can be obtained in C. This could be faster only if
it was written in machine language.
To test the speed advantage obtainable through registers, compile the
following program. To measure the speed of the program you must use
the registers as often as possible and should not use other functions
since they only extend the time required. For this reason the program
does nothing more than count a variable down from 5,000,000 to 0.
/* countdown. c 16.4.1 */
♦include <stdio.h>
void main ()
{
printfC'Time comparison with and without register\n") ;
printf ("RETURN for Start\n") ;
getchar ;
printf ("%cStart without", 7);
without_register () ;
printf ("%cStop!\nregister routine\n", 7) ;
printf ("RETURN for Start\n");
getchar () ;
printf ("%cStart with", 7) ;
with_register ( ) ;
printf ("%cStop!\n\n", 7) ;
147
16. Storage Classes Amiga C for Beginners
)
with_register ( )
{
register long i =5000000; /*Count from 5,000,000 to */
while (i — )
)
without_register ( )
{
long i = 5000000;
while (i— )
/
)
The preprocessor command #include includes the stdio.h file in
this C program. This file is required because the getchar routine is
used to obtain a character from the keyboard. In the Lattice C compiler,
the function is unusable because it waits for the <Return> key after
every character. However, it is sufficient for the program above, so it
can be used to wait for the <Return> key.
Timed by hand, the author counted 51.6 seconds without register
variables and 24.1 seconds with register variables. That's
impressive because it's twice as fast when the word register is used.
It should be noted that the multitasking capability of the Amiga, which
could have been performing a task in the background, was not used.
This would have provided a different result
148
Abacus 16.5 Local
16.5 Local
local Local variables arc the reverse of global variables. Different vari-
variables able groups such as register, auto or static local can be
defined. They are only valid in the block or the function in which they
were created. A local variable has precedence over a global vari-
able, which means that, if two variables were defined with the same
name, the local variable is used. The local variable gets preference
while the global variable disappears for the moment An example:
/* local. c 16.5 */
int 1 = 1;
void mainO
<
int i = 2;
printf <"%3d", i) ;
{
printf ("%3d", i) ;
(
int i = 3;
printf ("%3d", i) ;
} ■ .
printf ("%3d", i) ;
)
printf ("%3d",i) ;
testO;
printf ("\n\n n ) ;
)
test ()
{
printf ("%3d", i) ;
(
int i = 4;
printf ("%3d'\ i) ;
The numbers 2, 2, 3, 2, 2, 1 and 4 are displayed sequentially. In the
main function a new local variable is declared so that the global
variable i is no longer addressable. The following block keeps this
configuration and another 2 appears. Then another block follows in
which another i variable is defined. Because of this, the previous block
becomes invisible to the program and the current one prevails. The
result of the output is 3. After the program leaves all blocks, the hidden
variables appear again. The previous variable with the value 3 is erased
by leaving this block then disappears. The test function is now called
and proceeds to output i. Since no local variable is known at this
149
16. Storage Classes Amiga C for Beginners
point, the output of the global variable, which is 1, is used. Finally
a local integer variable is activated which overshadows the global
variable again. This ensures that the last variable defined in a block is
used, and that often used names (e.g., i or j) are recognized as runtime
variables in many loops as different variables.
150
17.
User-defined
Libraries
Abacus 17. User-defined Libraries
17. User-defined Libraries
One advantage of programming in C is the modular construction of
programs, which can accept existing functions used in other programs.
The #include directive lets you add external files that have frequently
used functions to the current program before compiling. The compiler
processes one large file instead of several small files.
Every C programmer writes his own functions at some time or another.
You've already entered two functions (strlen and strcpy) ; let's
use these. Most compilers contain these functions. However, viewing
them can give us an understanding of how user written functions work.
Save these functions to your own file under the name string.c. You
can include these functions in your own programs using the
♦include directive. The following line searches the main directory
for the include file string.c:
finclude "string.c"
The following line also adds the string, c file to the main file:
tinclude <string.c>
Of the two syntaxes, the second line is much more flexible than the
first, since it searches many different directories for the same file.
Most C implementations have include files as standard equipment
Files with .h extensions contain mostly #def ine directives. You can
find these functions in a library such as amiga.lib or lc.lib.
include files can be included on demand. The syntax reads:
♦include <file.h>
Before starting with include, first you need something that can be
included. A useful function can be written to compare strings. Since
strings are not elementary data types, they can't be compared with:
if(stringl == string2) /* This is wrong! */
If you wrote the variables stringl and string2 as character arrays,
the name would correspond to the address of the first element
(& stringl [ ] ). Therefore, the addresses of the two arrays always
differ. Since both arrays have been assigned by the compiler to separate
memory locations for their char entries, the comparison is completely
useless. The only case (theoretically) in which this i f test can be
fulfilled is if one or the other variable was defined as a pointer and if the
pointer pointed to the same string. This method doesn't work.
153
17. User-defined Libraries Amiga C for Beginners
17.1 The s t r cmp Function
You now have to write a program to compare each element of the first
string one at a time with each element of the second string:
strcmp(s,t)
register char *s, *t;
{
while <*s == *t)
{
if (!*s)
return (0); /* End reached (*s == 0) */
s++;
t++;
}
return (*s - *t) ;
The st r cmp function compares the characters of the s string with
those of the t string. As long as the characters are alike (*s == *t),
the while loop executes. A test determines whether the last character
matches the \ marker EOS (end of string). If so, both strings must be
identical, since s and t end with EOS. Otherwise the pointers move to
the next element and the process repeats.
If a character appears within s which differs from the t character, the
while loop terminates and the difference between the two characters
(*s - *t) returns to the calling program. Negative values indicate that
the s string was smaller than t. Positive values mean the opposite. A
null returned after the if test indicates that both strings are completely
identical.
Store this function and the other two files below as stringf unc.c.
Since the older strlen routine could be improved, we will use
pointers this time. Instead of the indices, the pointer moves over all
entries of the string up to the EOS character. The start value must be
stored first so that the number of increments can be computed. That is
faster than counting with an additional variable. The stringf unc.c
file therefore appears as follows:
/* stringfunc.c 17.1 */
strcpy(to, from)
register char *to, *from;
<
while (*to++ = *from++)
)
154
Abacus 17.1 The strcmp Function
strlen(s) /* Conversion to pointer! */
register char *s;
<
register char *help = s; /* Store initial position */
while (*s)
s++;
return (s - help);
/* Difference between pointers is Element number */
}
strcmp (s,t)
register char *s, *t;
{
while (*s == *t)
{
if (!*s)
return(O); /* End reached (*s == 0) */
s++;
t++;
)
return (*s - *t) ; /* Difference between two strings */
}
Now let's see if they function properly. For this you'll use two strings
which are initialized in the program.
/* stringtest.c 17.2 */
♦include "stringfunc.c"
/* Global arrays can be initialized! */
char stringl[] = "Hello!";
char string2[7] = { 'H\ "e\ '1', '1', 'o\ '!', 0);
main ()
{
printf ("\nComparison of >%s< and >%s< is %d\n",
stringl, string2, strcmp(stringl, string2));
printf ("Now >%S< and >%S< Result in %d\n\n",
stringl, "Huhu!", strcmp(stringl, "Huhu!"));
)
First we will look at the expected results of the function call strcmp.
The first call returns zero since both strings are really equal. The second
function call returns -16. This number is the result of the comparison
of the e and u characters. This means that the first different character in
the string ("Hello!") is smaller than the first different character in the
second string ("Huhu").
Array initialization is new to this program. Until now each element
was stored individually, automatic variables wouldn't allow storage
in any other form. With global variables, a string can be initialized
155
17. User-defined Libraries Amiga C for Beginners
directly, or, as in the second example, every character is initialized
separately. In the first example there wasn't even an indication of how
many elements stringl [ ] should have. This is another indication
that the C language was invented for those who consider laziness a
virtue. The compiler must determine the number of the character on its
own. It initializes stringl with 7 elements (don't forget the null
byte at the end). Those who prefer, can indicate the value as in the
second example.
If you assign the elements individually (example 2) to the fields, they
must be contained in braces and separated by commas. For multiple
dimensions, multiple braces must be used.
int f
ield [ 4 ] [ 4 ] =
{
{ 1,
2,
3,
4 ),
{ 6,
3.
4,
9>,
{ 3,
4,
5,
6 >,
{12,
9,
0,
2 >,
};
This formulation assigns field [ 4 ] [ 4 ] the proper values where the
first values { 1, 2, 3, 4 } are stored in the fields field [ ] [ ] to
field[0] [ 3 ] . The inner braces are not required on some compilers
and the directive could appear as follows:
int field[4][4]= { 1, 2, 3, 4, 6, 3, 4, 9, 3, 4, 5, 6,
12, 9, 0, 2 );
When some elements are not initialized, they don't have to be listed.
All elements left out are automatically assigned a null.
in field [3] [3]= {
{ 3, 2 },
{ 4 },
{ 3, 4, 5 },
);
The fields field[0] [2], field [1] [1] and f ield [1] [2]
contain nulls. A semicolon must follow the definition. After the inner
braces and the last brace there must be commas. Remember that initial-
ization only affects global or static variables, not auto vari-
ables.
156
Abacus 17.2 Itoa
17.2 Itoa
Another routine seen frequently in connection with strings is itoa
(Integer TO ASCII). It converts an integer value into the corresponding
character string. When you pass the number 123, itoa returns the
string "123" in a character array. This is very important when preparing
text that contains numbers. All conversions usually performed by
print f can also be done with user routines.
The itoa function requires, as parameters, an integer value which it
can convert, and a string to store the result. The head of the function
definition reads as follows:
itoa(n, s)
char s [ ] ;
int n ;
Conversion The modulo operator % performs the conversion. By dividing the
number by 10 you obtain the last place. Then the code for the number
'0' is added to get the first character. The number is then divided by 10
to shift it left one space and the last number drops off. The same
procedure is performed on the new last position. The program section
for this process appears as follows, if the index for the character array is
called i:
do
s[i++] = n % 10 + 'OS-
while <<n /= 10) > 0);
The last place is converted and stored in s until the number which was
stored in n has reached through constant division. The sign should
not be forgotten since it could cause problems for the loop (number
larger than 0). The simplest process makes the number positive before
the conversion and, if necessary, sets a flag for a negative value. After
the completed conversion, the suing returns the minus sign.
The completed processing converts the number 123 into the string
"321", but only the last place is processed and stored in the string. The
solution to this problem is very simple. Write another function that
reverses the string. Assuming that such a function already exists (see
the next section for the function) the routine appears as follows:
157
17. User-defined Libraries Amiga C for Beginners
/it****************************************/
/* Name: itoa */
/* Parameter: n(int), s (string) */
/* function: Convert Integer to string */
/* comment: Requires reverse () */
/A****************************************/
♦define EOS '0'
♦define FALSE
♦define TROE 1
itoa(n, s)
register int n;
register char *s;
{
register int i = 0;
register int sign = FALSE;
if(n < 0)
(
sign = TRUE;
n = -n;
)
do
s[i++] = n % 10 + 'O';
while (n /=10) ;
if (sign)
s[i++] = '-';
s[i] = EOS;
reverse (s) ;
)
Program The large header contains important information. The function devel-
header oped by the user should be ready for use when it is finished. After some
time the function name and the parameters to be passed may have been
forgotten. At that time you could consult the header with its comments.
The function can be compiled independent of other functions. If the
compiler permits it, it can be stored in a library. Of course the source
files can be included into the current file with:
♦include "itoa.c"
This increases compiler time, of course.
Since this function should be accepted in the library, it should be the
latest state-of-the-art. This can be done with the itoa function by
defining all variables as register variables. The define required for
this function should not be omitted, even if it appears somewhat cum-
bersome to determine a define for a single application. It improves read-
ability since larger programs usually access these macros.
158
Abacus
173 Reverse
17.3
Reverse
The reverse
function
Now to the reverse function which can reverse a string passed to it
Construction of the routine doesn't present a problem. Two pointers, or
indices, are needed for the beginning and end of the string. These point-
ers exchange their elements between themselves and are then moved
toward each other. The pointer at the beginning is incremented and the
one at the end is decremented. Exchange continues until the two point-
ers are equal, i.e., point to the same element. The routine is presented
complete with a commented header.
/****************************************/
/* Name: reverse */
/* Parameter: s (string) */
/* function: Reverse string */
/* comment: Requires strlenf) */
reverse (s)
register char *s;
{
register int c, i, j;
for(i=0, j
{
c = s[i] ;
s[i] = s[ j] ;
s [ j] = c;
}
)
strlen(s) - 1; i < j; i++, j — )
The strlen The strlen function initializes the index j, which should point to
function the last element of s. Every C compiler package has strlen included
in one of its libraries, or you can use the strlen function defined in
the previous chapter. Both routines (itoa and reverse) should be
stored in the library labeled itoa.c since it will be accessed later.
Please note that the itoa routine also comes as standard equipment
with most C compilers. These standard everyday functions have already
been written by others.
159
18.
C Features
Abacus 18. C Features
18. C Features
We have mentioned many times that C language is much more flexible
than many other languages. C has many features that BASIC doesn't,
and is still much simpler to use than assembly language.
This chapter examines some components of C which aren't possible in
other languages. These components are partly responsible for allowing
the user to take full advantage of C's speed and flexibility.
18.1 The ? : Operator
The ? : conditional operator evaluates the first statement and returns, if
the expression was true, the statement which follows. If the expression
was false (=), the operator returns the second statement following the
colon. This operator uses the syntax:
result = (expressionl) ? (expression2) : (expression3) ;
If expressionl is unequal to zero, expression2 becomes the
result. Otherwise expressions is returned. A concrete example:
c = (a>b) ? a : b;
This would be similar to the if construction:
if (a>b)
c = a;
else
c = b;
This term delivers the maximum of a and b. Since this is simple to
formulate, this operation usually determines minimum and maximum
quantity. The define:
#define MIN(a,b) ( ( (a) < (b) ) ? (a) : (b) )
#define MAX(a,b) ( ( (a)< (b) ) ? (a) : (b) )
Take a look at stdich which you'll find with your compiler. There
you'll find the definition.
163
18. C Features Amiga C for Beginners
18.2 The sizeof Function
The sizeof The sizeof (size of) function returns the sizes of objects (variables)
function regardless of type. The unit returned by this operator is defined on the
basis of the char elements. The following example followed by
sizeof (character) returns 1:
char character = 'a';
The result is always the number of occupied bytes for the object under
investigation. The following short program determines how much
memory is used by the various data types in your compiler. This will
tell you if an int variable occupies 2 bytes (most C compilers) or 4
bytes (Lattice).
/* sizeof. c 18.2 */
mainO /* Indicates memory required for data types */
{
printf ("\ndatatype\tmemory in bytes\n") ;
printf ("char\t\t%d\n", sizeof (char) ) ;
printf ("short\t\t%d\n", sizeof (short) ) ;
printf ("int\t\t%d\n", sizeof (int) ) ;
printf ("long\t\t%d\n", sizeof (long) ) ;
printf ("float \t\t%d\n", sizeof (float) ) ;
printf ("double\t\t%d\n", sizeof (double) ) ;
printf ("pointer\t\t%d\n", sizeof (char *));
164
Abacus
183 Brr Manipulation
18.3 Bit Manipulation
This section describes the remaining operators, which deal with control-
ling individual bits.
Operators for bit manipulations exist in addition to the logical combi-
nations. A bit (binary digit) represents a position in a binary number
and can therefore only assume one of two values (0 and 1). The conver-
sion into the binary system is similar to the conversion into the octal
or hexadecimal system. The bit is also the smallest unit which the
computer can use. It acts as the basis for all other numbers which can
be used in the computer. For example, a byte consists of 8 bits, a word
of 16 bits and a long word of 32 bits. A character can be stored in a
char variable. Characters are stored in bytes (8 bits); a byte can accept
256 different kinds of numbers. Depending on the compiler, an integer
value contains 16 or 32 bits and a long value 32 bits. Individual bits of
these data types can also be accessed. These operators cannot be used
with float or double variables.
18.3.1
AND
The and operator consists of the & character. Maybe you thought this
is the address operator. This character can be used for both purposes,
but it's hard to explain why this is so. You must know the context in
which it is used. If it is placed alone in front of a variable, it represents
the address operator. If it is placed between two values in a normal
arithmetic equation, then it is the binary AND.
The concepts logical and binary help you distinguish between two
completely different operators. The logical and is different from &&.
With and (&) individual bits can be reset. A set bit has the value 1, a
reset bit the value 0. The following table shows the connection between
various bit combinations.
Combining bits using logical operators
AND
OR
F.XOR
S
1 I
1
1
1
1
1
1
1
1
1
1
1
165
18. C Features
Amiga C for Beginners
According to the and a bit is set (1) when both bits are set, otherwise
the result is a 0. This is comparable with:
iftbltl == 1 &s bit2 ==1) /* Here is the logical AND! */
result_bit =1;
else
result bit = 0;
18.3.2
OR
With the (I) or operator bits can be set. A glance at the table above
will help you understand the various combinations of bits. In OR the
resulting bit is set if one or both bits were set. Only if both bits are 0,
is the result of OR also 0. The I sets individual bits and the & resets the
bits.
A mask acts as a storage area for the bits. A mask is represented by a
number placed over the value to be processed. If a variable is ORed with
this mask, all bits set in the mask are now also set in the variable.
Example: Bit number 2 should be set in the variable flags (the count starts at
0):
#define MASK 4
int flags = 73;
flags | = MASK;
After this operation, the OR with the value 2 2 (number of the bit to be
set) = 4 (sets the second bit in the variable flags).
A targeted resetting of certain bits sets the corresponding bits of the
mask to 0. With the and operation the desired zero bits are obtained.
Example: bits 1 and 4 should be reset.
int flags = 37;
flags s= 0355; /*A11 bits except 1 and 4 are set (0-7) */
Every bit has its own value according to priority. For example bit 3 has
a value of 8 (2 ). The table below shows the individual bit values:
bit Number
Value
4 5
16 32
6 7
64 128
Some examples for bit operations:
1 S 2 =
2 S 6 = 2
7 S 8 =
9 S 12 = 8
166
Abacus 183 Bit Manipulation
The last example should be examined closer in the binary system.
9 (dec) = 1001 (binary), 12 (dec) = 1100 (binary)
1001
S 1100
1000
1000 (binary) = 8 (decimal)
The same operation for OR:
1|2 = 3
2|6 = 6
7 I 8 = 15
9 1 12 = 13
The last line expressed
in binary:
1001
1100
1101
1101 (binary) •
= 13
(decimal)
It is important that the characters & and & & are kept separate from each
other. & connects expressions bit by bit && only makes a logical com-
parison from which either a 1 (true) or (false) is returned. Therefore 2
& 1 = 0,but2 && 1 = 1.
There is also a distinction between the operators I and I I . Loops and
conditions may result in strange behavior if you confuse these opera-
tors.
18.3.3 Bitwise Shift Operators
» « Operators for bit shifting are » and «. They permit bit shifting to
the left or right within a field. A shift to the left («) by one position
is the same as multiplying by 2, only it is much faster. All of this is
dependent on how data and numbers are stored and processed in the
computer. A shift to the right equals a division by 2. Depending on the
data type, either zero bits or set bits move into the free locations. For
unsigned values, zero bits are shifted in every case. For normal signed
int values it depends on the compiler used. For positive numbers, zero
bits should be added to the left, and for negative numbers, one bit. This
is compiler dependent and there is no guarantee of how this works.
167
18. C Features Amiga C for Beginners
The number of shifts is indicated behind the operator.
5 « 3 = 40
101 (binary) shifted left by 3 bits (zero bits are shifted in): 101000
(binary) = 40 (decimal).
Use the program in the previous section for converting decimal num-
bers to binary numbers.
18.3.4 EXCLUSIVE OR
The EXCLUSIVE OR operator * is related, as the name indicates, to the
OR operator. The only difference lies in the fact that both bits are set
The OR operation results in a set bit, but the EXCLUSIVE OR resets a
bit. The table for the exclus I ve OR is as follows:
EXOR 1
1
1 1
for example 2^1 = 3
Please do not confuse A with the up arrow for exponentiation. This
does not exist in the C language.
Remember: The bit is set only if both bits are different.
18.3.5 One's Complement
The one's complement operator ~ requires only one parameter. All bits
of the parameter are reversed. Set bits are unset and vice versa. It is
recommended to use this operator only for variables which were defined
as unsigned, or the sign is also affected.
unsigned number = ~3;
In the variable all bits except for the first one are set (priority and 1 =
1 + 2 = 3) so that the variable now receives the following bit sequence
(starting from a 16-bit integer):
1111 1111 1111 1100
= 65532
168
Abacus l*- 4 GoTO
18.4 Goto
Perhaps goto sounds familiar from BASIC, but the C implementation
is a true curiosity. This statement has a bad reputation in C, since it
can destroy a well structured program. Jumping in a function can defeat
the purpose of clarity in programming. Nevertheless the goto state-
ment is not totally useless. It can be used effectively in error trapping.
If an error occurs within several loops, which makes progress impossi-
ble, only the goto statement offers escape. The usual break directive
can only stop one loop, not several at once. Some tests and other break
commands could also terminate all loops. It is preferable to use goto.
The use of the goto statement of course assumes a label (a marked line
to which the goto jump should be made).
label: printfC'This is where goto will Jump!\n");
if (error)
goto label;
The labels can be defined in the program text anywhere, but must
include a colon. They are only required for the goto statement and are
formed exactly like variable names.
Note : The label and jump commands must be used in the same function. It
is not possible to jump across all functions.
169
19.
Complex Data
Types
Abacus
19. Complex Data Types
19. Complex Data Types
Now that we've listed all the important commands, we now come to
the extra capabilities of C. Among these are data types which can be
configured according to the needs and demands of the user.
19.1
Struct
struct (
char firstname[20] ;
char surname[30] ;
int age;
double income;
int sex;
} person;
The person This function defines the variable person. The variable person
variable consists of several partial variables which are described in more detail
within the braces. The first name has 20 characters, and the last name
30 characters. There are also fields for age, income and sex. Similar to
arrays, many entries are collected under one name. The difference is that
different variable types appear within the structure. Accessing individual
parts of this variable requires more specification than arrays, which use
an index. The structure uses either the . (period) operator or -> opera-
tor. An assignment of 30 to the element age appears as follows:
person. age = 30;
All other fields can be accessed in the same manner:
person. sex = 0;
person. income = 300000.0;
strcpy (person. fir stname, "Rena") ;
strcpy (per son. surname, "Bebewicz") ;
In order to use a pointer on such a construction, you must indicate the
data types. All you've done so far is create a complete variable. You
need a name such as int or float, through which other variables
such as a pointer can be defined. If several variables or pointers are used,
it would be better to create another data type which also has its own
name. This can be done by indicating the type name after the struct
statement. If it is called person, the uppercase letter indicates that it
isn't a variable. Since variables, statements and functions must appear
173
19. Complex Data Types
Amiga C for Beginners
Pointer
operators
Comment:
in lowercase letters, and defines in uppercase and lowercase letters,
structures can use a combination of the two:
struct Person {
char firstname[20] ;
char surname [30];
int age;
double income;
int sex;
} person;
A pointer to this structure can now be initialized for access:
struct Person *pointer;
To access one element of the structure, the expression would be:
(*pointer) .age = 30;
The parentheses above control the higher precedence of the ( . ) operator.
Usually a special operator is used as illustrated below:
pointer->age = 30;
This operator, made of a minus sign and a greater than character, is
easier to read. In addition, the arrow better illustrates its purpose (it
"points to" something).
All operations which affect basic data types, such as defining arrays
(vectors), can be used on the newly created structure. The line below
provides 100 structures for storing partial variables:
struct Person occupant [100] , *occ_upa;
Addressing individual entries can be done through an index (occupant
[3] .income = 25000.0), or after initializing the pointer with:
occ_upa = occupant;
The name represents the address of the first element. The following
could be written as an alternative:
occ_upa = Soccupant [0] ;
The pointer can also be used to access the entries:
(pointer->income = 25000.0)
The pointer can be used to search the entire array. The following
example sets the pointer to the first free element, provided that in an
unused entry the value zero was stored in age:
while (pointer->age)
pointer++; /* searches all entries */
Further applications of the struct directive will be discussed later.
174
Abacus 19.2 Bit Fields
19.2 Bit Fields
The last remaining data type is the bitfield. Bit fields are really a form
of structure definition. Unlike regular definitions, bit fields are usually
taken apart rather than created. A variable is defined which consists of a
certain number of bits. This variable always represents whole numbers.
The value range depends on the number of bits used. This number can
be calculated with the formula 2 number - of - Wts . These fields are arranged in
int objects so that the maximum field width is 16 bits. This also
applies to Lattice C which usually has a different concept of int. If a
field doesn't fit into the partially occupied integer value, it goes into the
next one. A lot of memory can be saved by clever selection of the field
width.
struct {
unsigned sex : 1;
unsigned married :
1;
unsigned children
: 4;
} data;
As in other structure definitions, the data types are placed inside braces.
To ensure that the bit field contains unsigned whole numbers,
unsigned is used (an abbreviation for unsigned int). A colon
separates the fieldname from the field width in bits. The definition
above occupies 2 bytes (size of a 16-bit integer), but is not completely
utilized. Since only 6 bits are used (1 + 1 + 4), an additional 10 bits
can be assigned for other applications without requiring additional
memory:
struct {
unsigned sex : 1;
unsigned married ; 1;
unsigned nr_children ; 4;
unsigned age ; 7;
unsigned nr_cars ; 3;
} data;
Additional data has been stored which occupies only 2 bytes. Access to
each bit field occurs with the ( . ) operator.
data.nr_children =2;
The limited values must be respected, since in this definition no family
can have more than 15 (2 -1) children or operate more than 7 (2 -1)
vehicles.
175
19. Complex Data Types Amiga C for Beginners
19.3 Unions
A special variable exists in C which accepts all conceivable data types.
This union is dimensioned by the compiler in a way that allows it to
accept all data types indicated in the definition.
union Oniversa {
in 1;
double d;
struct Person;
char c[100];
result;
All data types indicated can be stored in result. It is useful to
remember what type is stored, for example:
result = 2.8;
or
strcpy (Sresult, c) ;
The memory requirements of such a variable depends of course on the
length of the largest entry. In the example above this would be 100
bytes used by array c. Please note that only one type can be stored in
this variable. The author hasn't yet found a reason for using union
structures instead of solving the problem with other C data types.
176
Abacus 19.4 Enum
19.4 Enum
The C word enum defines a data type which assigns constant values to
the variables. Short for ENUMeration, enum lets you assign a consis-
tent integer number (constant) to a variable. This is useful for assigning
numbers to strings. The following example assigns numbers to the first
three words in color and a specific value to the black variable.
Finally, the assignment to the white variable continues where the
number assigned to black left off:
/* Definition of such a Data Type */
enum color (red, green, blue, black = 9, white)
/* variable Definition */
enum color var, *color_ptr - svar;
var = blue
if (*color_ptr == green)
*color_ptr = black;
The enum type assigns an integer value to each name starting at zero
and adding one for each element. With direct assignment values can be
skipped. The values defined in color are:
red
green
1
blue
2
black
9
white
10
177
19. Complex Data Types Amiga C for Beginners
19.5 Typedef
The typedef feature can be used to create new data type names. A
name assigned with this command can be used as another data type
during the definition. The program below gives the word float the
same meaning as the double data type:
typedef double FLOAT;
The advantage of this directive is that typedef permits changes in the
entire program similar to define. Also large data types can be
abbreviated with this command. Look at the example below:
typedef char * STRING;
All pointers to char elements can be defined simply with the word
string. The typedef command has an advantage over the
#def ine directive in that the definition of the replacement occurs in a
different way. One text can be replaced with another text. A blank
marks the spot in which the text replacement appears. The redefinition
of type STRING into another word isn't possible since everything after
the space behind char already counts as replacement text. With the
typedef command this is just the reverse. The last string STRING is
the replacement for the data type char *. It or the blanks in the middle
always belong to the definition of the data type.
This concludes the introduction to C keywords. These statements can
now be used in smaller programs. Practice makes perfect. Experiment
by changing one or more parameters in the programs to determine the
effect upon the program. Write your own new programs once you've
gotten used to entering the ones already listed above.
178
20.
Important Concepts
Abacus 20. Important Concepts
20. Important Concepts
20.1 Declarations
Declarations declare the data type of a variable or function in a program.
Various declarations have already been used. Directives can appear in
which you have to guess the data type that was declared, unless you
examine the expression for certain rules. First, some simple examples
(the first three are also definitions):
int i; Integer variable
float array [10] Float variable
double *ptr; Pointer to double element
long funcO; Function which returns a long value
Every declaration basically contains an elementary data type (char,
int, float), which in certain cases can be augmented by a special
storage class (auto, extern, register, static), or through
attributes such as long, short and unsigned.
extern double sin(); function from another file
returns double-value
static short digit small Integer variable
register long i; long-variable stored in a
register
Each name can also be equipped with combinations of *, D or even 0-
The asterisk to the left of the name represents the pointer character.
Parentheses and brackets appear to the right of a name. They should not
contain values during declaration, because that turns the declaration into
a definition ([] for arrays and for functions). Combining all parts of a
declaration can result in some complicated combinations:
long *field(); function which returns pointer to
long value
int *i_ptr[]; Field of integer pointers
float (*berech) (); Pointer to function which
returns float value
char *(*text)(); Pointer to function which
returns pointer to char
int * (*text_arr [] ) () ; Array of pointers to functions
which return pointers to int
181
20. Important Concepts Amiga C for Beginners
Complicated expressions are formed with unified rules. Going through
them step by step makes the routine work later to decode such combina-
tions. You'll need the table of operator precedence found in the Appen-
dices. From this you can see that the parentheses have higher priority
than the pointer.
Look at the first example listed above:
long *field() ;
Decoding First, the variable field is a function. Look at the left side of the line
expressions for the asterisk which defines the expression as a function. This
function returns a pointer. No additional information exists beyond the
parentheses. The left side of the line identifies the data type long.
Together this information creates a function which returns a pointer to
the type long.
After processing one side of the line, the information to the right of it
must be processed (if priorities permit). The last and most complex
example looks like this:
int * (*text_arr [])();
It looks complicated. It can be easily decoded by following the proce-
dures as listed above, but the description will take a little longer.
Start with the name text_arr. First test which operators are pro-
cessed first according to priority (to the right or left of the name). These
are the brackets which indicate an array. The operator has been processed
on the right; now go to the left A pointer there indicates that this is a
pointer array. The right side of the line informs you that the pointers
should point to functions (the parentheses are required because of the
high priority of parentheses over the asterisk). Changing sides again,
you note that the function returns pointers. Since on the right side there
is no additional information, continue on the left with the data type.
There it shows that the pointers point to integers. This line declares an
array of pointers to functions which returns pointers to int. Compli-
cated expression, complicated sentence; but simple to analyze.
Only data types which cannot be used in definitions as values for pass-
ing are prohibited. For example, no function can be declared which
should pass structures, arrays or functions. Pointers to such objects are
permitted and are the only way to access this information.
182
Abacus 20. Important Concepts
Comment: Some new compilers also permit structure passing. This may differ
from one compiler to another. The expression & structure is always
the address of the structure, but structure can represent different
things. In the older compilers this represents the starting address, like
the expression with the address operator. If structure is passed
with a compiler that can already pass the data structure, the entire data
field is made available to the calling function (not just the 4 bytes
which represent the pointer to it).
183
20. Important Concepts Amiga C for Beginners
20.2 Initialization
This word should also look familiar from earlier chapters. Before you
continue, here's a brief reminder of just what initialization does.
This. expression designates the first value assignment of a variable.
Before using a variable, it must contain a defined value. Otherwise the
result of calculations may be nonsense, or the system may crash. The
initialization can be a direct assignment in the following form:
int i ;
i = 0;
Or condensed into one line:
int i = 0;
The initialization in the definition has the advantage of not requiring
additional assignments to set the variable. This saves time and memory.
Declarations, definitions and initializations can be combined with one
datatype:
double number, pi = 3.1415926, sin();
C permits any constants and expressions during the initialization. The
following assignments can be found in one line:
long number = x * pi - abs (y) ;
char *cp = string + strlen (string) ;
The variables used were already initialized or number would have con-
tained an undefined value.
Braces can improve visibility for arrays and structures, and separate
individual entries from each other. A pair of braces must be placed
before and after the data which are transferred to the variables. A comma
follows the fields, even if the braces were used. After the initialization
there is a semicolon which is often omitted, causing compiler errors.
Some examples for correct structure definition:
struct CAR {
char make [16] ;
int hp;
int cylinder;
double price;
};
struct CAR will have =
184
Abacus 20.2 Initialization
{
"BMW",
120,
4,
40000.0
>;
Or collected together through the structure definition:
struct CAR {
char make [16] ;
int hp;
int cylinder;
double price;
} will_have =
{
"BMW",
120,
4,
40000.0
);
The examples of multi-dimensional array initialization were already dis-
cussed in the chapter about arrays and pointers. Limitations because of
memory classes were also mentioned. Initialization is only permitted
for global, external or static variables. If an auto variable
appears within a function which corresponds to this initialization, e.g.:
char messaged = "Remember the Initialization!";
This can be fixed with a pointer definition:
char *message[] = "Remember the Initialization!";
There are no limitations if the lower definition is used as a pointer vari-
able. Another possibility is the use of static variables. It doesn't
matter whether the string is stored in a static or auto variable.
One small word, but a big difference.
static char messaged = "Remember the Initialization!";
185
21.
Pointer Arrays
Abacus 21. Pointer Arrays
21. Pointer Arrays
You worked with pointers and arrays in earlier chapters. As the title
indicates, they can be combined to construct an array of pointers. You
may be wondering what you can do with a pointer array. If you market-
ed an existing program in a foreign country, you'd have to find every
piece of text in the source code and translate the text into that foreign
language. It would be simpler and safer to store all the text in one area
of the program, or even in a separate file, and let the translator change
it from there. A pointer array would point toward that area or file.
Let's start with a list of error messages that the user might see after
entering incorrect input. The use of error numbers makes sense, since
some errors occur at several different locations. In the current program
portion, passing the error number to the error routine is sufficient
because the function should do the rest
One solution to this problem would be a function that tests the occur-
rence of this error or another error, and display a message if necessary.
error (e_number)
int e_number;
{
switch (e_number)
(
case 0:
puts ("Everything OK, no error!");
break;
case 1:
puts ("Wrong key activated!");
break;
case 2:
puts ("Please insert diskette!");
break ;
default:
puts(Unknown error occurred!");
}
)
puts This is a fairly complex implementation of the function which requires
another puts call for each additional error message. The puts func-
tion displays a string on the monitor, without the options available in
printf. It is a little faster than the general output functions, but
various case statements must be added, which slow down the pro-
gram. Since every number can be assigned a certain error message
(string), it should be possible to use the error number as an index to a
field of strings. Since a string is usually stored in char error [81],
the memory for the text is defined as a two-dimensional array:
189
21. Pointer Arrays Amiga C for Beginners
char error [32] [81] ;
Now there is space for 32 strings with a maximum length of 81 charac-
ters each. This formulation permits the following routine for error
message output:
error (e_number)
in e_number;
«
puts (error [e_number ] ) ;
)
But the work which was saved here, must be completed elsewhere. Each
string must be initialized with the strcpy function. The following
command sequence shows how:
strcpy (error [0] , "Everything OK, no error!");
strcpy (error [1] , "Wrong key pressed!");
strcpy (error [2] , "Please insert Diskette!");
It doesn't matter whether text is called with strcpy or puts. A
disadvantage of this method is that memory gets allocated elsewhere.
The definition allocates 81 characters, including a null byte for every
error message, even if a message only requires 20 characters. This
doesn't matter too much in the Amiga, but the user shouldn't develop
bad programming habits. If you do the same thing for a text in which
each word is assigned an entry, memory rapidly fills with garbage.
As a last resort, the string arrays can solve almost all the problems
mentioned above. The definition of a string array is as follows:
char *error[32);
The pointer can be set to the beginning of an error message and can
make the message length dependent on a fixed array length. The next
string starts immediately after the last character of the previous string.
This avoids initialization.
You may remember that a program in Chapter 15 pointed to a string
within program text. This can occur during pointer definition; the entire
pointer array is initialized with the starting addresses of the strings. The
error messages must be defined as global if this turns out to be the
case:
/* error_msg.c 21 */
char *error[] =
{
"Everything OK, no error!",
"Wrong key activated!",
"Please insert Diskette!"
};
190
Abacus 21. Pointer Arrays
main ()
{
/* Display all error messages */
int i, error_msg = sizeof (error) / sizeof(char *) ;
ford = 0; i < error_msg; i++)
printf ("Error Number %d: \"%sV'\n", i, error [i] );
}
Since the number of error messages are not counted, they aren't indi-
cated during the definition. Because of this, additional text can be
entered between braces without making changes. In the actual program,
however, the number must be calculated. The memory requirement of
error can be obtained from sizeof. The error function is now an
array of pointers. Now sizeof reports that the variable consumes 12
bytes. That is the memory requirement for any pointer, and has no bear-
ing on the memory needed for the text The 12 bytes are divided by the
space requirement of a char pointer (which is 4 bytes). The result is
the number of pointers, the maximum index minus one (The indexes
start with 0).
191
22.
Useful Macros
Abacus 22. Useful Macros
22. Useful Macros
Much work has already been done with #def ine. The substituted text,
called a macro, was kept simple; one word exchanged for another. But
that's only half the job, macros also allow you to pass arguments.
Some useful macros have been developed to make parameter passing
easier for the user.
Construction Functions that do little and have concise coding can be written as
of a macro macros. Since macros replace the original text, the compiler translates
the C code directly to machine language at that location. Function calls
or parameter passing is not required. The required directives are located
at the exact location in the program. This makes the macros faster and
more efficient than function calls. If used frequently, however, macros
make the program code much larger. The same operations are repeatedly
stored in identical form at the exact place where they are needed in the
program code. An advantage of macros is that they are usually
independent of data types. This condition can be seen in the example of
the MAX macro created earlier in the book:
♦define MAX(a,b) ((a>b)? a : b)
If variables il and 12 have been defined as integers, the following
macro results:
result = MAX(il,i2);
From the preprocessor
result = <(il>i2)? il : i2);
The variable result is also an integer value. If 11 and i2 were
defined as float values, the same expression occurs, but a float
number is returned for result. In text replacement it doesn't matter
which data type was used. This is impossible with functions because
the data types are specified for parameters that are passed. This is
extremely easy to use.
195
22. Useful Macros Amiga C for Beginners
2 2.1 Macro Error Sources
Improperly implemented macros harbor some dangers which can lead to
errors. These errors can be extremely difficult to detect, but most can be
prevented with little effort.
If the macro call just defined included some parameters which contained
operators, errors could appear. For example:
result = MAX(il | 2,i2);
is converted as usual into:
result = <<il I 2>i2)? il | 2 : 12);
The > comparison operator has a higher precedence than the I character.
This means that first a test is made to see whether 12 is less than 2.
The result of this logical comparison (0 if false, 1 if true) is then com-
bined with il using OR, bit by bit. This could not occur in the basic
calculations since they have a higher precedence than the comparison
operators (see the Appendices for a table of all precedences). A simple
remedy is to place all parameters found in the macro inside parentheses.
Use this definition:
#define MAX(a,b) <(<a)>(b))? (a) : (b) )
Side-effects caused by calculations and value changes can also cause
problems. A simple example is the following short program which
should calculate the squares of numbers between to 10.
/*bad_macro.c 22.1 */
#define QUADRAT (x) ((x)*(x))
main ()
{
/* Wrong use of a Macro */
int i = 0;
while (i <= 10)
<
printfC'The square of %d ", i) ;
printf("is %d\n", QUADRAT (i++) ) ;
}
}
The output of the program is:
The square of is
The square of 2 is 6
The square of 4 is 20
196
Abacus 22.1 Macro Error Sources
The square of 6 is 42
The square of 8 is 72
The square of 10 is 110
Where's the mistake? Examine the material left by the preprocessor for
the compiler. The line with the macro is the important line:
printfC'is %d\n", QUADRAT (i++) ) ;
It becomes:
printfC'is %d\n", ( (i++) *(i++) ) ) ;
If the square of 2 (i=2) is computed, the following expression is what
was actually calculated and passed to the print f fiinction:
The variable is incremented before the multiplication, and the second
multiplier is wrong.
You may have wondered why the program uses two printf calls
instead of making do with one. There is another error source here which
must be considered as a separate entity, otherwise this overview would
not cover all possible side-effects. To demonstrate the errors which
occur in printf functions, let's try this with the same function, but
without a macro:
main ()
(
/* Wrong use of a Macro */
int i = 0;
while (i <= 10)
{
printf ("The Square of %d is %d\n", i, i * i++) ;
}
As a result you get two squared numbers which don't match the desired
numbers. 4 is offered as 3's square (the square is only calculated for the
preceding number). This is caused by the parameters being placed on the
function's stack (temporary storage), where the function expects to find
them. Unfortunately the storage of these values occur in reverse order,
i.e., first i * i++ is stored, and i is incremented. Then the first
parameter of i, which already has the wrong value, appears.
C language offers many routes to writing short and efficient programs.
However, there is a danger of the new programmer trying too much, too
soon. The side-effects shouldn't occur in functions and macros unless
you know their effects on all variables and parameters. Again, make use
of the precedence table as needed (see the Appendices for this table).
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22. Useful Macros Amiga C for Beginners
2 2.2 Library Macros
Frequently-used macros are best stored in a library, from which they can
easily be inserted in source code with tinclude. This group includes
various conversion functions for letters (e.g., testing if a letter is upper
or lowercase). The following defines have the following tasks:
Convert uppercase letters into lowercase letters:
♦define to_lower(c) ((c) +32)
Convert lowercase letters into uppercase letters:
♦define to_upper(c) ((c) -32)
Test for letters (yes = 1, no = 0):
♦define isalpha(c) ((c»='A" ss (c)<='Z' || <c)>='a' s&
<<=)<«■ z')
Test for uppercase letters (yes = 1, no = 0):
♦define isupper(c) ((c>>='A' && (c)<='Z")
Test for lowercase letters (yes = 1, no = 0):
♦define islower(c) ((c>>='a' SS (c)<='z')
Test for number (yes = 1, no = 0):
♦define isdigit (c) ((c»='0" ss (c)<='9')
Test for alphanumeric characters (letters or numbers) (yes = 1, no = 0):
♦define isalnum(c) isalpha(c) II isdigit (c) )
Test for blank, tab, linefeed, carriage return, formfeed (yes = 1, no = 0):
♦define isspace(c) ((c)==' ' II (c)=='\t' ll(c)== '\r' ||
(c)=='\n' II (c)=='\f)
Test for special characters (yes = 1, no = 0):
♦define ispunct(c) ((c)>=* ' ss lisalnum(c) )
Test for printable characters (yes = 1, no = 0):
♦define isprint(c) (<c)>=040 ss (c)<=0176)
198
Abacus 22.2 Library Macros
Test for control characters (yes = 1, no - 0):
tdefine iscntrl(c) <(c)>=0 SS (<c)==0177 II <<=)<• '))
Test for ASCII characters (yes = 1, no = 0):
tdefine isascii(c) ( (c) >=0 SS (c)<0200)
These defines should be easily understood once they are examined.
They should be written into a fde named CTYPE.H, unless this type of
file is already available in a subdirectory. If the following line occurs in
a program, you know what should be found there:
♦include <ctype.h>
Remember that for the test for letters, only the 26 letters of the
alphabet are considered. International special characters are not viewed as
letters. Maybe they can be implemented in a suitable manner. Perhaps
the strcmp can be converted with the new defines.
char *s, *t;
int n, compare;
compare = strcmp(s, t) ;
compare = strncmpfs, t, n) ;
compare = stricmp(s, t) ;
compare = strnicmp(s, t n) ;
The first function is identical to the routine you programmed. It com-
pares two strings and returns the result of the comparisons. In the
second function strncmp, the third value indicates up to what point
the comparison should be made. The comparison can be limited this
way to n characters. For example only the first four elements. The
functions which have an i in the name, don't differentiate between
upper and lowercase letters. Comparing the two strings "aBcDEf ' and
"ABcdeF' with the function returns the value zero because both strings
are equal.
199
23.
Communication
Abacus 23- Communication
23. Communication
The programs written so far have only displayed data on the screen or
requested keyboard input. It's time to communicate with other devices.
The CLI is the easiest way to transfer data. In this chapter, we'll
communicate with the CLI as well as other devices.
2 3.1 Passing Data with the CLI
All programs are called from the CLI by entering the filename and
arguments (if needed). Here is one type of call to invoke ED:
ED file.c SIZE 50000
This complete line can be made available to the called program, though
not in this form. The operating system modifies this line slightly.
Now comes the question of data transfer. The main function containing
two arguments controls this. Until now every call appeared as follows:
main ()
The next code passes two values from the calling program from either
the CLI or a make file. The first value represents the amount of
information and a pointer to a char pointer. This sounds somewhat
complicated, but looking at the input line of the program should make
it clear. First the new version of main with two arguments:
maln(argc, argv)
int argc;
char *argv [ ] ;
{
}
The name of our fictional program is prg. Look at this sample entry:
prg Textl parameter 3 -pi
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23. Communication Amiga C for Beginners
After the program call, the variable argc contains the number of argu-
ments (5). Why is 5 passed when only 4 arguments are available? The
fifth argument comes from adding the program name used during the
call. The name argc (ARGument Count) is a random choice, since it
is an auto variable of the main function. The name argv (ARGu-
ment Vector) handles vectors.
Spaces or tabs separate every argument of the input line. After the call
the pointers of * argv [ ] point to:
argv[0] "prg"
argv[l] "Textl"
ar gv [ 2 ] " P ar amet e r "
argv[3] "3"
argv[4] "-pi"
Let's examine the data. Use the following program to print the data:
/* arg_test.c 23.1 */
main (argc, argv)
int argc;
char *argv [ ] ;
{
while ( — argc >= 0)
puts (*argv++) ;
)
What can be done with this? You can access a small math program by
entering the following in the CLl:
compute 123.5 * 4711
The following program is written so that it will only perform simple
calculations consisting of two numbers and an operator. Feel free to
improve on the program as needed.
/* arg_math.c 23.1 */
extern double atof(); /* Declaration */
int error =0;
main (argc, argv)
int argc;
char *argv [ ] ;
{
double result, value ();
if (argc != 4)
printf ("\nWrong Entry\nCall: numberl # number2\n") ;
else
{
result = value(argv[l], argv[2], argv[3]);
if ( ! error)
204
Abacus 23.1 Passing Data with the CLI
printf("\n%s %s %s = %.91f\n", argv[l], argv[2],
argv[3], result);
)
}
double value ( number 1, op, number 2)
char *numberl, *op, *number2;
<
double zl = atof (numberl) ;
double z2 = atof (number2) ;
switch (*op) /* only the first character */
{
case ■ / ' :
return (zl / z2) ;
case ' * ' :
return (zl * z2) ;
case '-' :
return (zl - z2) ;
case '+' :
return (zl + z2) ;
default :
printf ("\nUnknown Operator >%s<\n", 7, op);
error = 1;
return (0.0) ;
}
}
Lattice The mathematical function/floating point library must be linked to the
standard library because it contains the atof function. Example:
lc -Lm math2
Aztec If you work with Aztec C, the mathematical function/floating point
library must be linked to the standard library C.LIB since it contains
the atof function. Example:
cc +L math2 .c
In math2.o -lm -lc
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23. Communication Amiga C for Beginners
2 3.2 Buffered Input/Output
Many programs require permanent data storage for files, whether it is a
database or a word processor. These require routines that control input/
output with external devices such as printers, disk drives, RS-232 inter-
faces or a hard disk drive. The operating system provides various func-
tions for this purpose. These routines can be divided into two groups;
buffered input/output and unbuffered input/output.
This type of data transfer does a lot of work, even though it may not
seem evident at first For example, all data selected for transfer to disk
goes to a buffer first. When this buffer completely fills, the data goes to
the disk. The question is, why do it this way?
A disk drive reads and writes information much slower than the com-
puter can send or receive it This is caused by the mechanics of the disk
drive. Before writing any data, the read/write head must move to the
track where the data is stored. Then it must wait until the disk rotates to
the right location. Only then can data be written. Although this timing
is brief in human terms, the computer (actually its central processing
unit or CPU) is kept waiting a very long time.
Disk buffers If you transmitted every character with this method, the computer would
spend more time waiting to place a single character on the disk drive
than performing any other task. For this reason, smaller amounts of
data move to an area of memory in the computer before transmission.
Once this buffer fills, the data moves to the disk drive. This reduces
computer waiting time. As soon as the drive writes the first character to
the proper place, it can place the other data right behind it and write the
complete buffer in one pass. This reduces the number of disk accesses,
which accelerates program execution. The same principle is also used
for reading data.
The functions which perform this job are getc and putc, which like
their relatives getchar and putchar, input or output a character.
These functions are not part of the C language. For this reason they can
be found in a library, or in this case as a define in a header file (.h).
The definition of getc and putc can also be found in the stdio.h
file with the familiar putchar and getchar.
•define getc (p) (— (p)-> _ront>=0? » (p)->_ptr++:_filbf (p))
•define getchar () getc(stdin)
♦define putc (p) (— (p) -> _wcnt>=0? * (p) ->jptr++= (c) ) ) :_f lsbf ( (c) , p) )
idefine putchar () putc(c, stdout)
206
Abacus 23.2 Buffered Input/Output
Let's clear some of this up. The definitions of put char and
get char are all you need to know for now. Both can be traced back to
getc and putc and represent special versions of the two functions.
Before the first character can be moved with these functions, a channel
must be opened. A channel is just a data line to a certain device. No
cables actually open up a channel, but the system knows where to send
the information. A special code obtained from the operating system
during the opening of the channel allows addressing the device at any
time. Devices and individual disk files can be addressed.
Several files can be addressed on the same drive without having data
conflict The file pointer indicates the channel. Since a buffer is used for
input/output, the computer must be informed of where the data should
be stored intermittently and how large a space must be reserved. A
structure named file (notice the uppercase letters) defined in stdio.h
contains all necessary data for buffered input/output. The following list-
ing writes a file and men reads it again:
/*fprint-fscan.c 23.2.1 */
♦include <stdio.h>
main ()
{
FILE *input, *output, *fopen();
char filename [81], text [200);
printf ("Please input file name!\n");
scanf ("%80s", filename);
printf ("Input a (long) word!\n");
scanf ("%200s", text);
output = fopen (filename, "w") ;
printf ("Filehandle %d\n", output);
fprintf (output, "%s", text);
fclose (output) ;
input = fopen (filename, "r") ;
printf ("Filehandle %d\n", input);
f scanf (input, "%200s", text);
fclose (input) ;
printf ("The Text: >%s<\n", text);
)
The fopen The fopen function opens the channel and returns the file pointer,
function used for all future access, to this file. Since fopen returns something
other than an integer, it must be declared as a function which returns a
file pointer. This routine requires two arguments: the name of the file
and the access mode. The user can enter the name. The access mode tells
the computer what should be done with the file. The mode can be one
of three letters:
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23. Communication Amiga C for Beginners
r (read) opens a file for reading
w (write) opens a file for writing
a (append) opens a file for adding additional data
A file opened for reading (r) can only read data, not write data. A file
open for writing (w) lets you write data. The append (a) mode writes
data to the end of an existing file. In normal write (w) mode, writing
starts at the beginning of the file and overwrites existing data. This can
easily lead to loss of data. The example above overwrites an existing
file and destroys some previously stored data.
After the opening, the file is ready for writing. The file handle appears
on the screen. The scanf function assigns the characters entered
through the keyboard to the string text. The f print f function can
write data to a file. It is almost identical to the printf routine, but
differs in the first argument. Before the command string, a file handle
must be passed to assign the information to the correct file. After
writing, the file closes. This step is very important because of the
buffer. All input/output goes there for intermediate storage until the
buffer is filled. Some of the data input can still be stored in that buffer.
If the user assumes that everything was stored on the disk and switches
off the computer, the data still in the buffer would be lost. For this
reason the f close call closes the channel after writing the remaining
buffer contents to the open file.
Now the file reopens again, but this time for reading which is signaled
with mode (r). Since keyboard input always uses scanf, the f scanf
is used here. First the file pointer and the arguments of the scanf
routine must be passed to the read function.
The correct closing of the file follows. If you omitted this instruction,
data loss cannot result. However, it's good practice to close an opened
file immediately after use, not only because it is good housekeeping,
but also because a computer can maintain only a certain number of
open files. If more files are opened, a channel cannot remain open at a
certain time. Should an error occur, because the operating system
cannot make a channel available, the file pointer is returned as zero.
This happens when no channels are available, or the file which should
be read does not exist.
The next example program is a small copy program. It is called with
arguments and therefore is able to accept arguments from main.
One difficulty must be avoided. Nobody knows in advance what type of
data will be transmitted. The f scanf cannot be used since it has to
indicate if strings or numbers are used. The program can only read one
character at a time. The scanf routine with the format instruction %c
can be used, but the f getc function works much better. It reads a
character from an input file and is much faster than the f scanf
function. The fputc statement performs the output
208
Abacus
23.2 Buffered Input/Output
After opening the two files, a character is read and displayed immedi-
ately, until. . .. You don't know when all data has been copied. How can
you detect when the last character has been read? The problem has
already been solved, f getc returns a special character if no additional
information is available — end of file (EOF). The #include file
stdio.h contains this text as a define so that the incoming charac-
ters only have to be compared with EOF.
eof is stored there as -1. This has consequences which at first are not
evident Valid data have codes which in f getc are between and 255.
When -1 appears, no char variable can be selected to accept the charac-
ter. Either negative numbers are ignored or data is lost. For this reason,
int variables are used even if only a char element is stored in them.
/* copier. c 23.2.1 */
♦include <stdio.h>
main(argc, argv)
int argc;
char *argv [ ] ;
<
long copyO; /*If it is interesting */
if (argc !=3)
{
printfC'Bad Arguments ! \n") ;
printf ("From_file to_file\n") ;
}
else
copy(argv[l] , argv[2]);
copy (fromfile, tofile) /* Copy Routine */
char *fromfile, *tofile;
<
FILE *input, *output, *fopen();
register long counter = 0;
register int c;
if ( ! (input = fopen (fromfile, "rb") ) )
/* Open as Binary file */
{
printf ("%s can not be opened!\n", fromfile);
return OL;
)
if (! (output = fopen (tofile, "wb") ) )
(
printf ("%s can not be opened!\n", tofile);
fclose (input); /* Was OK */
return OL; /* Zero */
while( (c = fgetc(input) ) !=EOF)
{
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23. Communication Amiga C for Beginners
fputc( c, output);
counter ++;
)
f close (input) ;
f close (output) ;
printf ("\n%ld Bytes copied!\n", counter);
return (counter) ;
)
This copy program is called as follows:
copier [d:] [\path]namel [ .ext] [d. ] [\path]name2 . [ext]
Everything written into the brackets is optional and can be omitted.
Only two filenames must be provided. If an error should occur during
the opening of the two files, an error message appears. An error mes-
sage is also displayed if too many or too few arguments are passed.
Since it is very slow, this program is unsuitable for everyday use.
However, it's a suitable demonstration program. Let's limit the
discussion to the essentials. The files are opened as binary files with rb
and wb (Aztec compiler users should omit the b; the file always opens
as a binary file). For example, this prevents any conversions being
attempted which could occur in text files. During reading all \ r
characters (carriage return) are erased automatically and characters with
code 26 (<Ctrl><Z>) are converted to EOF. During write the linefeed
(\n) is converted to a character combination (\ r\n). Opening the file
with the appendix b (binary) returns all characters as they are stored in
the file. During the write all characters sent are stored in the file and
not converted.
210
Abacus 23.3 More Buffered Input/Output
2 3.3 More Buffered Input/Output
Besides f getc, f putc, f scanf and f printf there are some other
important functions that use the internal buffer. Among them are
f read and f write. These routines transport any number of bytes.
For this reason two additional arguments are required for f read and
f write. One argument is the area which serves as the buffer and the
other the size of the units to be transmitted. This needs some explana-
tion. The buffer in previously used functions was always located in the
FILE structure. Since only small amounts of data were transported, the
buffer did not have to be large (512 bytes). Since the user can now
determine how much data is transmitted, this buffer may be too small.
For this reason the user must define the memory area, thereby setting
the maximum size of the data transfer. The data size must also be indi-
cated. In getc and putc only one character can be transmitted (1 byte)
and the size of the char object doesn't have to be indicated. If a long
value, instead of a character, is stored, 40 bytes must be transmitted for
10 of these values. The object size (in this case four bytes each) is the
second argument that must be passed. If the data type is unknown, the
si zeof operator should be used because it returns the correct value.
Besides these two arguments, the number of units to be transmitted
(char, int, structure, ...) and the file pointer must be transmit-
ted. The buffer size determined at the time of definition should not be
too small. A call of this function appears as follows:
Datatype buffer [Element] ; /* Definition of the buffer */
f read (buffer, sizeof (Datatype) , Element, f ile_ptr) ;
The first argument is the buffer from which the data is read. The buffer
should be the same type as the units to be transmitted. The second
value is the unit size. This unit is a data package which can be trans-
mitted as one item. If long variables are transmitted, it makes sense to
indicate 4 bytes as data block length, since 4 byte units are the normal
memory requirement. If 100 double variables are stored, 100 is placed
at the element. Finally a file pointer is added, which was received from
fopen.
If data is read or written, the argument sequence and type remains the
same. The f write function stores the data using this syntax:
int table [876], size = 876;
FILE *outpt_ptr;
fwrite (table, sizeof (double) , size, outpt_ptr) ;
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23. Communication Amiga C for Beginners
If the value of size is not specified, either through a variable or with a
define, the sizeof operator can be read:
sizeof (table) /sizeof (int)
The function returns the number of completely transmitted data pack-
ages. This ensures storage of all data. During copying data can be read
until the number of requested data differs from the data delivered. If
f read returns a zero, the last data was read. A sample program:
/* fread.c 23.3 */
#include'<stdio . h>
#def ine NOM_DATA (sizeof (data) /sizeof (long) )
Long data[] =
(
4711, 815, 1024, 1, 31415926, 0, -13, 10,
OxFFFF, 065432
);
main ( )
{
FILE *input, *output, *fopen();
int i;
long test [NUM_DATA] ;
char filename [81] ;
printf ("Please input filename! \n") ;
scanf ("%80s", filename);
printf ("Data size %d. Elements %d\n",
sizeof (data) , NUM_DATA) ;
output = f open (filename, "wb") ; /* binary! */
fwrite(data, sizeof (long) , N0M_DATA, output);
f close (output) ;
printf ("Read Data!\n");
input = f open (filename, "rb") ;
printf ("%d Elements read\n",
fread(test, sizeof (long) , NUM_DATA, input));
fclose (input) ;
ford = 0; i < NUM_DATA; i++)
printf ("%ld\t", test[i));
printf ("\nDone!\n") ;
This program writes a long array to the file after entering the filename.
The array size and the number of elements appear on the screen. The
define NUM_DATA stores all data on the disk. After closing the file,
another array accepts the data read. All data appears on the monitor.
Lattice C users must open the file as binary, or internal conversion
produces false values in the variables. If f write and f read are used,
the file must also be opened as a binary file.
212
Abacus 23.4 Unbuffered Input/Output
2 3.4 Unbuffered Input/Output
Besides the buffered functions just demonstrated, there are other routines
which do not require a buffer. The data to be transmitted don't have to
be stored in a buffer, but can be stored immediately. This cancels all the
effort required for the buffer and internal pointers. This also cancels the
need for a file pointer through which the operating system can access
the buffer. A channel number assigned during the opening must be used
as identification. This channel number is stored in an integer variable
and replaces the file pointer in all calls. The open function opens a
file. Filename and file mode (as an integer) arguments pass to the
function. In f open the mode must be a string, while in open the
mode is one of three values: 0, 1, 2 or 8. These numbers correspond to
the strings r, w and a.
opens a file for reading
1 opens a file for writing
2 opens a file for reading and writing
8 opens a file for appending
Instead of these numbers defines can be used to make the program
more readable. They are stored in a header file named f cntl.h and are
defined as follows:
#define 0_RDONLY
ttdefine 0_WRONLY 1
#define 0_RDWR 2
#define 0_APPEND 8
To use these defines, the file must be included in the source with the
sequence:
♦include <fcntl.h>
Another difference from the f open routine is that open always
assumes the existence of a file. The following call creates a file even if
the file already exists:
fopen ("filename", "w")
The open function always prompts for the name of an existing file.
The create function must be used to create a new file.
The create function returns an integer (the file handle). You don't
need to call open. If an error occurs and the file cannot be opened, both
create and open return the value -1. Before using the returned value
as a file handle, check the file handle for a value of -1, or the system
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23. Communication Amiga C for Beginners
will crash. The key combination <CtrlxCommodorexAmiga> resets
the computer, but deletes any data in the RAM disk.
A file opened in this manner allows writing using the write function
instead of the f write function. Since this method uses no buffer,
only certain input/output functions can be accessed. Also, the read
function replaces the f read function. Buffered functions have an £ in
front of their name (e.g., f open, f read, f close). Unbuffered func-
tions omit the f . The close function closes an unbuffered file.
The following function stores a list of double numbers.
/* write-read.c 23.4 */
#define NUMBER (sizeof (data) /sizeof (double) )
double data[] =
{
1.5, 2.0, 3.14159265, 2.718281828,
);
main ()
{
int handle, dummy = 0, i, actual;
double data2 [NUMBER] ;
char filename [ 81 ] ;
pr int f ("Please input filename ! \n") ;
scanf ("%80s", filename);
handle = creat (filename, dummy); /* Create new */
if (handle != -1) /* Everything OK? */
{
actual = write (handle, data, sizeof (data) ) ;
printf ("Desired %d Bytes, Actual %d BytesXn",
sizeof (data) , actual) ;
close (handle) ;
)
else
printf ("Error during creation of %s\n", filename);
handle = open (filename, 0, dummy); /* Read */
if (handle ! 1) /* Everything OK? */
{
actual = read(handle, data2, sizeof (data) ) ;
printf ("Desired %d Bytes, Actual %d BytesXn",
sizeof (data) , actual);
close (handle) ;
)
else
printf ("Error during opening of %s\n", filename);
for(i=0; i < NUMBER; i++)
printf ("%.81f ", data2[i]);
printf ("XnThat's all!\n");
214
Abacus 23.4 Unbuffered Input/Output
The open and create functions, which return a file handle, have a
peculiar variable named dummy. This variable represents a value which
may be unnecessary, but the compiler checks for this variable if needed.
The value stored in dummy, as the name suggests, has no significance.
In open the second argument represents the dummy value for reading
or writing.
The write and read functions have one less argument than f write
and f read. Furthermore (and this is important), the file handle is
placed at the beginning, not at the end as in the buffered functions. The
unbuffered functions transport the data one byte at a time only. This
means that the size indication is unnecessary. The return value is the
number of bytes transmitted so far.
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23. Communication Amiga C for Beginners
2 3.5 Direct Access
The following functions provide the user with the ability to directly
access certain characters in a file. The difference from the usual read
lies in the fact that not every character must be read starting at the
beginning of the file until the program finds the particular characters.
To access the last ten characters in a file of 1,000 characters, 990 char-
acters would have to be read first. With direct access, the command
starts the reading after the 990th character. A file pointer always points
to the last accessed data. During a sequential read or write, when
one character after another is processed, this pointer always increments
by one. The functions lseek and f seek let the user set this pointer
to any desired position. Both routines require three arguments for this,
where lseek is the unbuffered version and f seek the buffered
version. For this reason lseek requires the file handle as the first
argument, while f seek expects a file pointer. A second value follows
the number of bytes by which the pointer must be moved. Positive
values move the pointer toward the end of the file, negative values
toward the beginning of the file. This value must be passed as a long
value. The third argument, an integer, indicates from which position the
movement should start. A sets the data pointer to the beginning of
the file, 2 to the end of the file and 1 to the current position. Some
examples:
lseek (f_handle, 100L, 0) ;
The data pointer moves to position 100 (i.e., 100 characters from the
start of the file). It now points to the 101st byte of the file. The follow-
ing function places the pointer at position 70, since the call passed the
value 1:
lseek (f_handle, 70L, 1) ;
The 1 indicates the calculation of the new pointer position from the
current location. To move the pointer 20 characters toward the begin-
ning of the file, the following function is required:
lseek (f_handle, -20L, 1);
If the processing of a file should start from the end of the file, the
pointer can be set to the last position of the file with:
lseek (f_handle, 0L, 2) ;
This shows that in mode 2 (end of the file), only negative numbers or
are permitted since the pointer is already at the end of the file. In mode
0, only positive numbers or can be used. These functions only move
216
Abacus 23.5 Direct Access
the file pointer. The data must be read or written with the various func-
tions such as read or write.
The lseek function returns the value of the data pointer after the
move, f seek returns either or -1. With -1 an error occurred, other-
wise everything proceeded without a problem.
Two additional routines, a buffered and an unbuffered version, can sense
the current value of the data pointer. Since it is a long value, the
f tell and tell functions must be declared first. The only required
argument of both functions is the proper file handle.
The function call could be replaced with the call:
lseek (fjiandle, OL, 1);
which indicates the value of the current data pointer.
217
23. Communication
Amiga C for Beginners
2 3.6 Reading a Character
The getchar
function
Our previous programs used scanf to read a character from the key-
board. The problem with this is that you have to press the <Return>
key after every character. A word processing program would be
intolerable under these conditions. Even a modest application such as
controlling the cursor in all four directions would be difficult
The getchar function offers help. This function receives the pressed
key's code immediately. Even here there is a difference between theory
and practice. Almost all other C implementations use this function
according to rules — except for the Amiga. The Amiga requires the
<Return> key for execution.
23.6.1
Standard Input/Output
Usually data is entered through the keyboard into the computer. Mes-
sages and the results of calculations usually appear on the screen. These
two devices combined are called the console. If you do not instruct the
computer to get the source data from or send the destination data to a
particular device, it defaults to the standard input/output (keyboard and
screen). The good news is that these devices can be changed by the user.
The Amiga can input data from another device instead of the keyboard.
Standard The standard input device is the keyboard. The standard output device is
devices the monitor screen, or screen for short. In various windows the output
defaults to the CLI window. This window is the standard output for
your previous programs. All CLI limitations also apply to your pro-
gram. This causes the error in getchar.
The CLI is line-oriented. Data processes after you enter your input and
press the <Retum> key. Anything can be typed in without the com-
puter reporting, during input, that this isn't permitted. Press
<Ctrl><G> to make the screen blink. Even though these characters can
be entered, you cannot display them on the screen. If you try this, the
blinking function executes. The CLI is an input console which
processes whole lines and not single keys.
This rule of using only complete lines also applies to programs started
from the CLI. Now that you know why <Return> must be pressed, it's
time to create a user-defined window to solve this problem.
218
Abacus 23.7 A User Window
2 3.7 A User Window
Creating a personal window is fairly simple. Developing your own
window consists of opening an output file, since the output is written
into this newly created window. The keyboard then acts as the input
device, according to the arguments set by the user window.
23.7.1 The Three Windows
You have three device options for opening non-CLl windows:
CON:
RAW:
These strings follow the open command in the CLI. They replace the
usual filenames and drive specifiers. The asterisk sends data directly to
the CLI window; a new window isn't created. Nothing has changed for
the input either. Opening an asterisk device only causes the same
trouble as before.
The CON: device creates a user window. The open call as listed below
creates an unbuffered open file and a pathname of CON:
open("CON:0/0/200/50/Title line", 0, dummy)
The CON: device name replaces the drive specifier, and the new
window's coordinates follow. Finally the name Title line appears
in the upper left corner of the title bar. A slash character (J) separates
the window arguments. The other arguments such as (read) and the
dummy value follow the usual syntax of the open routine.
The returned file handle appears in the examples with all read calls.
An 81 -character string acts as a buffer. Try this short routine:
/*windowl.c 23.7.1 */
♦define c *character
♦define ESC 27
main ()
{
int dummy = 0, num, handle;
char character [81] , line [256];
219
23. Communication Amiga C for Beginners
handle = open ( n CON:0/0/200/50/My Program", 0, dummy);
printf ("Opens %d handle\n", handle);
if (handle != -1)
{
do
{
num = read(handle, character, 1);
printf ("Character >%c< Code %d\n", c, c) ;
) while (c !=ESC);
close (handle) ;
}
If you forget to test for a successful opening of a file, the computer
may crash using -1 as handle value. When the program executes, a new
window appears; nothing happens after you press a key. All keys are
processed only after you press the <Return> key. A new window
appears. Unfortunately the window only works in line mode, like the
normal CLi window. Press <EscxReturn> to exit the program.
The raw: option also creates a window. The difference between this
option and CON: is the way the information is displayed. A raw:
window displays information in "unfiltered" form (i.e., control
characters and garbage appear). Change con: to raw: in the above
example. Compile, link and run this new version and watch what
happens next
Again a new user window appears. You can size this window and move
it around the screen. Select the new window and send data to it (type on
the keyboard). Notice that the window reacts to every keypress. How-
ever, the input doesn't appear in the user window. The program seems
to be ignoring the RAW: specification.
All output with printf continues to go to the CLI window. This
isn't surprising since it's the standard output device for programs started
from the CLI. To write something into the user window, for which a
special handle has been issued, a write routine must be used. Instead
of printf , use f print which has the same functions.
Wait a minute. The f printf function is a routine for buffered files
and an unbuffered file was opened with open. It only works if the file
handle was obtained with f open. Since the handle is an integer value
and not a file pointer, the handle doesn't fit the f printf . However,
the library contains a command named sprint f. Instead of writing
the prepared data into the standard output of the buffer, everything goes
to a string. The following example invokes this function:
char string[200]; /* not too small */
int test = 4711;
sprintf (string, "The result is %5d\n", test);
220
Abacus 23.7 A User Window
Now the user can write anything into his own window — the print f
function isn't required for output into the CLI window. Now every-
thing needed for input/output in the new window is available. Here is
the corrected listing:
/* window3.c 23.7 */
tdefine ESC 27
main ( )
<
int dummy = 0, num r handle;
char c, line [256];
handle = open ("RAW:50/50/200/60/My Program", 0, dummy);
pr int f ("Handle %d open\n", handle);
if (handle != -1)
(
do
(
num = read(handle, Sc, 1) ;
/* write(handle, &c, 1); output only the character*/
sprintf (line, "Character >%c< Code %d\n", c, c) ;
write (handle, line, strlen (line) ) ;
} while (c !=ESC) ;
close (handle) ;
}
221
23. Communication Amiga C for Beginners
23.8 Redirection
The operating system controls the redirection of data so the programmer
doesn't have to worry about it The use of standard input/output acts as
the condition for ensuring data redirection. This includes familiar func-
tions such as printf , scanf , putchar, getchar, puts, etc.
Look again at the first RAW program above which used printf for
text output. This example will help you understand redirection.
The "normal" call for programs not expecting arguments is:
program_name ,
Instructions that are executed by the operating system and not by the
program can follow the filename. The greater than (>) or less than (<)
characters precede these instructions. The characters inform the
operating system that the standard input/output should be modified.
Here's a practical example:
prg <filel >file2
The program never sees these two arguments. The operating system
reads the standard input from f ilel and sends the output to f ile2.
The operating system also opens and closes the files automatically. The
greater than (>) and less than (<) characters indicate the direction of data,
as an arrow would indicate direction. You can immediately see that the
data goes to the filename £ile2. Let's examine this process using the
window2.c RAW program in the previous section. The printf can
be redirected so that all text goes to a file or a printer (device prt:).
Start the program (called window2 here) with the following line:
window2 > output. data
The new window appears again but no keypresses seem to affect the
window. That's all right, since the output which would otherwise
appear in the CLI window now goes to the file output.data. After
typing on the keyboard for a while, press the <Esc> key. The window
disappears and the user returns to the CLI . The output.data file can
now be read using the type or ed commands.
Input can also be redirected from the keyboard to a file. This is how a
make file could be created. In these programming examples this
wouldn't make sense since you don't read from the standard input. A
redirection would not make much sense in this case.
222
Abacus 23.8 Redirection
The standard input/output is a normal line. Just as in opening a file, a
file handle is returned. Since these lines are always open, the program-
mer doesn't have to worry about them. There are of course variables for
these handles. They are:
stdin
stdout
stderror
The stdin variable represents "standard input" and the stdout vari-
able represents "standard output." What is the third?
In addition to the input and output of "normal" information, C offers an
error channel. This makes sense in the following situation.
As described above, the information is redirected. Because an error
occurred in the input (e.g., a nonexistent input file) an error message
appears on the screen. Wait, the standard output was written to another
file. This would mean that the error message was written to the file and
the user might not know about this error. For this reason error mes-
sages use a separate channel to display user messages.
All three variables (stdin, stdout and stderr) can be used as file
pointers which are returned through f open.
Caution: These buffered input/output routines should not be confused with the
unbuffered ones. Permitted functions with the file pointers above would
be fprintf, f write, f read, etc.
The definition of getchar can be found in the file stdich under:
getc (stdin)
223
24.
Tricks and Tips
Abacus 24. Tricks and Tips
24. Tricks and Tips
During programming unexpected errors can sometimes occur. For a
novice programmer, the reasons for these problems can be very hard to
find. Much work is often required to determine whether the cause of the
problem is in the source code, the compiler or the operating system.
This chapter has a few hints for helping you find those errors.
You'll find that this chapter contains a number of tips and tricks for C
programming on the Amiga. These tips include the creation of C
programs that are accessible from the Workbench, preprocessor
directives and macros.
2 4.1 Starting from the Workbench
You may have already tried to start your own C program from the
Workbench. Perhaps you wondered why, despite a full disk, nothing
appeared in that drawer's window. The reason for this is that every
visible program has an additional file used for storing the program's in-
formation and icon data. Every program which appears in a Workbench
window has a file with the extension of .info.
Our C programs also need .info files before they can be accessed from
the Workbench. Select a suitable icon on the Workbench (the clock or
Notepad, for example). Any other icon can be selected for this program.
Now enter the CLi. Copy only the source .info file to an .info file
for your file. Remember to use the .info extension for both files in
this command. The example below copies the Notepa&inf o file to
a new .info file for the file test-workb:
copy notepad. info test-workb. info
Change test-workb to your own filename, and remember to keep
the .info extension on both filenames.
Quit the CLI. Click the disk icon containing the target file and .info
file to display the icon. If the icon is covering another icon, move it to
a free location in the window. Click once on the icon. Press a <Shift>
key and click on a disk icon. Select Snapshot from the Special
menu to save the new position.
The following program will tell you how it was accessed, from the
Workbench or from the CLI.
227
24. Tricks and Tips Amiga C for Beginners
/♦access. c 24.1 */
tinclude "stdio.h"
main(argc, argv)
int argc;
char *argv [ ] ;
{ int dummy = 0, handle;
char line [256];
if (argc) /*Argument number not equal to */
{
handle = open ("RAW: 50/50/200/60/My Program", 0, dummy);
if (handle != -1) /* No Error on opening */
{
sprintf (line, "Started from CLI!\n");
write (handle, line, strlen (line) ) ;
while) — argc >=0)
{
write (handle, *argv, strlen (*argv) ) ;
argv++;
)
read(handle, line, 1); /* Wait for key press */
close (handle) ;
)
else
fprintf (stderr, "\nError in opening Window\n") ;
)
else
(
printf ("Started from the Workbench !\nRETURN-Key! \n") ;
getchar ( ) ;
)
)
It is important that the programmer know whether the program started
from the Workbench or cli. The argument counter arg senses this. If
arg=0, the user started the program from the Workbench. Consider the
possible values in the CL I. As a minimum, argc contains a 1 only
when the program name was used during the call without additional
arguments. Otherwise this variable is incremented by the number of
parameters. The is an ideal method of differentiation between the two
calls. The big question: "Who cares where the program started?"
Start the program window2, from the previous chapter, which opens a
window. The Workbench creates an additional, useless window. One
window is used, the other remains empty. There must be an option of
sensing a program start from the Workbench or from the CLI.
In the first case you get a window automatically and the standard input/
output is automatically directed to this window. The basic functions
such as scanf and printf can be used, and you can still enjoy the
use of your own window. In the second case, the user must handle his
own window and input/output.
228
Abacus
24.2 Other Preprocessor Directives
2 4.2 Other Preprocessor Directives
The directives #def ine and tinclude should be familiar to you by
now. Preprocessor directives make the programmer's work easier. The
most important are the following:
tundef MACRO
Undefining This is the opposite of #def ine. This undefines (cancels) the macro
definition. Assume that two #def ine directives had been used as
follows:
tdefine EOS
tdefine EOS '\0"
Any subsequent program sections use the most recent definition of
EOS. The first assignment is ignored for the moment. This process can
be compared with local variables which use the same name. Access can
only occur to the last variable (definition) defined. If the definition is
reversed with #undef , for example:
tundef EOS
the defined EOS is still present, but now with the first assignment (0).
Partial The following directive permits the compilation of certain portions of a
compilation file, depending on the macro that was defined:
#ifdef MACRO
Should the macro be defined, the following portion is processed by one
of these two preprocessor directives:
telseif MACRO
tendif MACRO
If the macro is unknown at this point, all lines are skipped up to the
following directives. If an telseif appears the subsequent source
code is compiled up to the fendif .
These directives are comparable to the C commands:
iff)
{
}
else
229
24. Tricks and Tips Amiga C for Beginners
The commands themselves have nothing to do with the final code. The
reversal of the process makes the following line possible:
#ifndef MACRO
Here the macro cannot be defined, so the part following can be com-
piled. Certain parts of a file can be included or left out through the
setting of a define, without changing the file to a great extent.
Where are the directives used?
In programs intended for compilation on other compilers or even other
computers, some differences must be considered such as compiler errors.
To achieve an error free compiler run, a define can indicate the
compiler type. These directives can be found in some header files which
come with the compilers.
230
Abacus 243 Finding and Removing Errors
2 4.3 Finding and Removing Errors
No program, in the initial stages of development, is free of either
syntax or logical errors. The compiler calls these syntactical problems
to your attention. Removing these errors shouldn't be a problem. This
section describes a few of the possible meanings behind these errors.
Missing semicolon
If the semicolon is not missing in the line indicated, check one or two
lines above the line stated by the compiler and check the level of paren-
theses.
Braces do not agree
This error often requires a search of the whole area preceding the error. If
you omitted a brace somewhere, the following part is added to the
function described up to this point. This in turn leads to mysterious
error messages, for example the missing semicolon in the next function
definition.
Wrong answers
If a function which executes flawlessly suddenly returns wrong results,
the error may be caused by a failure to declare the function (not for
int). For this reason all functions not having a return value of int
should be declared globally at the beginning of the file. The global
declaration keeps newly added functions, which also use this routine,
from enoring out Complex formulas which work with various opera-
tors and data types should generally be in parentheses. This not only
makes them more visible, but also prevents errors. Nobody knows all
the priorities of various operators by heart and this can quickly lead to
problems if a mistake is made. It is better to use one parenthesis too
many than one too few.
Easily confused character combinations
Even experienced programmers have misread these characters:
==and =
&& ands
I I and |
Watch for the legal maximum values of the various data types in calcu-
lations. They may differ from one compiler to another:
231
24. Tricks and Tips Amiga C for Beginners
char -128 to 127
int -32,767 to 32,766
long -2,147,483,648 to 2,147,483,647
38 38
float -10 to 10
^ ,_, ,„ 303 303
double -10 to 10
These can never be exceeded, even in intermediate results of a long equa-
tion such as:
i = (x * y * z - z) / y - x;
This can happen quickly with x * y * z if the three factors contain
large numbers.
System crash
This may have many causes. For example:
Pointer not initialized
Wrong parameter passed (wrong data types)
Pointer access to odd address (except for char pointer)
232
25.
System
Programming
Abacus
25. System Programming
25. System Programming
One of the reasons people work with C language is because of its
speed. The main reason Amiga owners use C is probably because the
Amiga's operating system was written in C. Knowing the peculiarities
of C often helps you understand the Amiga's operating system. This is
especially noticeable during system programming when you try to get
more performance from the computer.
Intuition This chapter takes you into the world of Intuition. Intuition is the
section of the operating system that is concerned with windows,
screens, icons, gadgets, menus and the mouse. Intuition's capabilities
are so vast that we can explore only a small portion of this material.
You'll find additional references suggested if you wish to explore
further. We chose to limit ourselves to introductory material on
Intuition, especially the creation of windows and screens.
One small warning in advance: Intuition is very complex. You'll see
this from the C source that follows in this chapter— the source codes
are much more complicated than the ones you've seen so far. Even if
you don't understand everything, you should try the programs and
experiment with them.
2 5.1 The Intuition Principle
To use Intuition in user programs, some conventions must be followed.
For example, Intuition routines can be used only when the Intuition
library has been opened. Intuition is simply a large library containing
the functions used in connection with windows and similar things. The
difference from the C libraries presented up to now is that these routines
are not linked during linking. The user relies on the fact that they are
stored somewhere in the computer and are available during program
execution. This has some advantages. Since many programs use the
same Intuition routines, they don't have to be stored several times in
the memory. Every program can use the routines for its own purposes,
even if they work with other programs in memory (multitasking). This
saves working memory. It makes no difference where these routines are
stored in the memory. When you open the intuition.library, a
pointer is returned to the beginning of this function list. A trademark of
Intuition programming is a lot of pointers and structures.
235
25. System Programming Amiga C for Beginners
2 5.2 A Window under Intuition
We displayed a window on the screen with the normal open function.
This function lets the user select the size and position in advance, and
permits window sizing and movement. However, Intuition offers
special features for windows. Let's look at the required structure which
contains all the important information for the window:
struct NewWindow
{
SHORT LeftEdge, TopEdge;
SHORT Width, Height;
DBYTE DetailPen, BlockPen;
OLONG IDCMPFlags;
ULONG Flags;
struct Gadget *FirstGadget;
struct Image *CheckMark;
UBYTE *Title;
struct Screen *Screen;
struct BitMap *BitMap;
SHORT MinWidth, MinHeight;
SHORT MaxWidth, MaxHeight;
USHORT Type;
}
The The structure definition can be found in the header file intuition/
NewWindow intuition.h. Now let's filter out the items that we are really going
structure to use. The name is already remarkable: NewWindow. The same file
usually contains a structure named Window. You need the
NewWindow structure to define a new user window.
The first four entries represent the upper left corner and the window's
dimensions in height and width. These are the same values as those
used in the CLl's Open command:
openC'CON^O/^O^OO/SO/windowtitle", 0, 0);
To use the same values for the Intuition window, the values are
assigned to the structure components. The following definition precedes
the window description:
struct NewWindow NewWindow;
NewWindow. LeftEdge =20;
NewWindow. TopEdge = 40;
NewWindow. Width = 200;
NewWindow. Height = 50;
236
Abacus
25.2 A Window under Intuition
The capabilities a CLi Open command can't provide are color settings
for the window.
The values in DetailPen specify the window title and the height of
the title bar. The number describes the color register index. If 4 possible
colors are available, they are numbered from to 3. The colors cannot
be changed because they're determined by the settings in Preferences.
The background always occupies register 0. The BlockPen register
draws the color for the window's border.
25.2.1
The Window Flags
Smart Refresh
Activate
windowsizing
windowdrag
windowdepth
Nocarerefresh
The next entry (iDCMPFlags) will be skipped since it isn't used. The
element Flags in the NewWindow structure determine certain items
in the window, which are set with defines. Every define deter-
mines whether or not an Intuition function is required (e.g., WINDOW-
S I z ING). Look at the defines used in the sample program.
There are many more useful defines included for windows.
This causes the Amiga to control and store everything concerning
window changes and contents. If another window is dragged over the
user window, a part of the window may be temporarily obscured. The
computer automatically stores this area in a buffer and, if needed, will
restore it again.
This automatically activates the window once its opened. This saves the
user the trouble of clicking the window to activate it
Permits a window with a size gadget to change dimensions. By select-
ing this define, the gadget appears in the lower right corner of the
window. The operating system keeps watch over this gadget for any
activity.
The window can be moved.
The window can be moved in front of or behind other windows with the
front and back gadgets (the gadgets in the upper right corner). The oper-
ating system keeps watch over these gadgets for any activity.
Practically anything that occurs during program execution can
selectively generate a message from the operating system. If you want a
message displayed when you try resizing a window, you can generate
one. For example, when editing a text using ED, the text file must be
updated when the window size changes. The program gets the message
that the window must be brought to the current condition. With the
define above, the operating system is told that no such message is
237
25. System Programming Amiga C for Beginners
desired. The message is not needed since SMART_refresh takes care
of all update work when active.
Of the remaining elements of the NewWindow structure, only Title
and the last five are of interest. As the name implies, the title is placed
into the title bar at the top of the window. The following program
demonstrates that only the address of the string is assigned:
NewWindow. Title = "The User window";
If no constants are used as in the example, the memory space must be
prepared by the user and its beginning assigned to the entry Title.
The values MinWidth.MinHeight.MaxWidth.MaxHeight
indicate the minimum and maximum values for the user window. The
user cannot go beyond these limitations. Since the maximum height of
a window is 200 or 400 pixels, these numbers are used more frequently.
PAL versions of the Amiga can create a maximum height of 256 or
512 pixels, depending on the mode selected.
Finally wbenchscreen is entered into the element Type so that the
parameters preset by the Workbench can be used.
25.2.2 Opening a Window
After this preliminary work, the window can finally be opened. The
Openwindow function opens the window and returns a pointer. This
pointer points to a window structure but shouldn't be confused with
NewWindow. It is more comprehensive than NewWindow and can be
examined in intuition.h.
The Openwindow function requires the address of the NewWindow
structure as the parameter. Since many compilers permit the passing of
whole structures, the following expression can be used to determine the
address:
' SNewWindow
If everything was processed properly, the new window will have the
specifications which were entered in NewWindow.
The CloseWindow function is all you need to close the window again
(e.g., when the program is finished). It has the window pointer as its
only parameter. The window disappears again.
Finally the Intuition library closes to leave everything the way it was
found. If you close Intuition before closing the last window, the Guru
Meditation appears.
238
Abacus 25.2 A Window under Intuition
25.2.3 A Window Program
This listing describes a large amount of theory. The program opens a
window which can be moved, sized and moved to the front or back.
Watch upper and lowercase letters in this listing.
/* window_intuition.c 25.2.3 */
/* From Amiga C for Beginners */
/* by Abacus */
♦include <exec /types. h>
♦include <intuition/intuition.h>
extern struct window *OpenWindow() ;/* Declaration */
extern long *OpenLibrary () ; /* Hello Aztec-User */
struct IntuitionBase *IntuitionBase;
♦define INTUITION_REV
main ()
{
struct NewWindow NewWindow;
struct Window *Window;
long i;
IntuitionBase = (struct IntuitionBase *)
OpenLibrary ( " intuition . library" , INTUITION_FEV) ;
if (IntuitionBase = NULL)
exit (FALSE) ;
NewWindow. LeftEdge =20;
NewWindow. TopEdge = 20;
NewWindow. Width = 200;
NewWindow. Height = 80;
NewWindow. DetailPen = 0;
NewWindow. BlockPen = 2;
NewWindow. IDCMPFlags = NULL;
NewWindow. Flags = SMART_REFRESH | ACTIVATE |
WINDOWSIZING | WINDOWDRAG | WINDOWDEPTH |
NOCAREREFRESH;
NewWindow. FirstGadget =■ NULL;
NewWindow. CheckMark = NULL;
NewWindow. Title = (UBYTE *)"The User window";
NewWindow. Screen - NULL;
NewWindow. BitMap = NULL;
NewWindow. MinWidth = 80;
NewWindow. MinHeight = 25;
NewWindow. MaxWidth = 640;
NewWindow. MaxHeight = 200; /* PAL - change to 256 */
NewWindow. Type = WBENCHSCREEN;
239
25. System Programming Amiga C tor Beginners
if ( (Window = QpenWindow (SNewWindow) ) — NULL)
exit (FALSE) ;
for(i = 0; i < 800000; i++) /* Small Pause */
CloseWindow (Window) ;
CloseLibrary ( Intuit ionBase) ;
exit (TRUE) ;
}
The program above exactly follows the indications and requirements
previously stated. First the Intuition library opens. If this is not possi-
ble for some reason, a is returned as an Intuition pointer. Continuing
would make no sense at that point so the program will end. The
window pointer returned can be null so it must be tested.
Examine the declaration of the OpenWindow function at the beginning
of the listing. This not only preserves a good C style, but also sup-
presses the changing of returned values with the cast statement. For
example, this is the case in the OpenLibrary because the routine
returns not only the Intuition pointer, but also a variety of other pointer
types. Nevertheless the function should be declared at least as a routine
which returns pointers. This prevents, for example, the Aztec system
crashes which result from not declaring the function. This means that
for the compiler, integer values will be delivered which in Aztec are
only 2 bytes long. It should be obvious that the value with 4 bytes
does not arrive. Only 2 bytes will be accepted.
The cast statement struct intuitionBase* can be used to
trick the best compiler. Most of the time the resulting value isn't equal
to and does not cause the program to crash. During the next access to
a library function with the IntuitionBase pointer, the system
crashes. This accident cannot occur with Lattice since its integers
always use 4 bytes.
During the opening of the library, the routine wants a version number
which is required for proper processing. If the system has the same or
later version, everything proceeds smoothly. Since this program has no
special needs, a is selected.
While opening the window, the address of the NewWindow structure is
passed. The system then accepts the data in an internal area so that even
this variable, NewWindow is no longer required. If something is done
to the window, it can be done with the window structure.
If the compilation displays warning messages, don't be alarmed. Some
structures need definition which are not used explicitly but appear in a
structure definition as sub-elements. Maybe the functions required can
be included with include. This may also result in additional
unknown structures surfacing which also want to be defined. The only
solution is to define all functions with include. This requires an
enormous amount of memory space, and increases the compiler time
240
Abacus 25.2 A Window under Intuition
significantly. Unless the user has a RAM disk on which all include
files are stored, it is not advisable to do this because nothing changes in
the object code anyway.
After the general framework of the window program has been con-
structed, some experimentation is helpful. Change a few values in the
NewWindow structure to see the effect on the window. Leave the
unknown structure entries and the type element untouched.
Under Intuition, it's impossible to exhaust the topic of windows. The
user who wants to know more should obtain more literature on this
subject
241
25. System Programming Amiga C for Beginners
25.3 Screens
A screen is simply a CRT (Cathode Ray Tube) display. In most PCs
and home computers, only one screen shows the screen contents. The
Atari ST and Amiga screens can display several windows at a time.
The Workbench screen is already familiar to you. Any number of win-
dows can be opened on any screen, depending on the amount of memory
available. It also determines the color composition and the number of
colors available to be used by the windows. The Workbench generally
offers 4 different colors and works with a resolution of 640*400 pixels
(640*512 pixels in PAL systems).
The user can specify these values for each program in order to construct
a screen to personal taste. The number of colors depends on the number
of available bit-planes. A bit-plane represents a part of memory which
is used for storing graphics. More memory permits more bit-planes and
therefore more colors. The Workbench uses two bit-planes for four
colors. A table illustrates the connection between colors and bit-planes.
Number of bit-planes
->
Number of colors
1
->
2
2
->
4
3
->
8
4
->
16
5
->
32 (not always possible)
Not only can the number of colors be selected, but also the resolution
of the screen. You can reach a maximum of 32 colors and a resolution
of 640*400 pixels (640*512 pixels in PAL systems.) As in the win-
dow, two color registers can be assigned, which are responsible for the
borders and the background. Since these values which are stored in the
NewScreen structure strongly remind you of the NewWindow struc-
ture, let's look at the structure definition.
struct NewScreen
{
SHORT LeftEdge, TopEdge, Width, Height, Depth;
UBYTE DetailPen, BlockPen;
OSHORT ViewModes;
USHORT Type;
struct TextAttr *Font;
tBYTE *DefaultTitle;
struct Gadgets *Gadgets;
struct bitMap *CustonibitMap;
'}
242
Abacus 25.3 Screens
The first entries in this structure have the same names as those in
NewWindow. They also have exactly the same meanings. Depth
indicates the number of bit-planes (1-5), which were already discussed.
DetailPen and BlockPen are the color indices. They depend on the
number of available bit-planes.
The next important entries are Type (the customscreen must be
set here) and Def aultTitle which points to the title line of the
screen. This is enough for the user program to fully define a screen.
The beauty of Intuition is that everything follows a certain pattern so
that many different problems can be solved in the same manner. After
understanding how to create a window, it shouldn't be a problem to
create a screen on the monitor. First the NewScreen structure is
stored in the manner described above. Then the screen is opened with
the following function:
Screen = Openscreen (SNewScreen) ;
The variable Screen represents a pointer to the structure named
screen. Also, the structures NewScreen and Screen must be
differentiated here. NewScreen is only required once for the
Opens creen function. The data is transferred to the Screen
structure (the Screen structure is much more comprehensive than
NewScreen). A pointer to the new screen structure is the return value.
To open a window to this screen, the initialization of the NewWindow
structure must be changed slighdy. The Type in the define WBENCH-
SCREEN is replaced by customscreen. The entry Screen must be
supplied with a screen pointer. The define CUSTOMSCREEN indicates
that the window to the user screen should be opened. The window gets
all the capabilities offered by the screen. Since several screens can be
opened by a program, the window must be attached to a specific screen.
This assignment can only be made after the screen has already been
opened and the screen pointer is available.
Before the program end the screen is closed with Closes creen to
which the screen pointer is passed. The window must be closed before
the screen, or serious problems will occur.
25.3.1 A Screen Program
The listing for the subject of screens has some more enhancements
which will be explained now.
/* screen_intuition.c 25.3.1 */
/* From Amiga C for Beginners */
/* by Abacus */
243
25. System Programming Amiga C for Beginners
#include <exec/types.h>
♦include intuition/intuition. h>
extern LONG OpenLibrary () ;
extern struct Screen *OpenScreen() ;
extern struct Window *QpenWindow() ;
struct IntuitionBase *IntuitionBase;
♦define INTUITION_REV
struct NewScreen NewScreen =
<
0,0,
640, /* Width */
200, /* Height; PAL version-change 200 to 256 */
3, /* 3 bitplanes = 8 colors */
3,5, /* another color combination */
HIRES,
CUSTOMSCREEN,
NULL,
"To end the program, please click Close-Gadget!",
NULL,
NULL,
};
struct NewWindow NewWindow =
{
40, 40, /* X and Y Position */
280, 120, /* Width, Height */
4, 6, /* Colors (0 - 7) */
CLOSEWINDOW,
WINDOWCLOSE | SMART_REFRESH | ACTIVATE | WINDOWSIZING
I SIZEBRIGHT | WINDOWDRAG | WINDOWDEPTH,
NULL,
NULL,
"*** Hello ***",
NULL,
NULL,
190, 20,
640, 200, /* in PAL systems change the 200 to 256 */
CUSTOMSCREEN
};
main ()
<
struct Screen *Screen;
struct Window *Window;
if ( (IntuitionBase = (struct IntuitionBase *)
OpenLibrary ("intuition. library", INTUITION_REV) )
== NULL)
exit (FALSE) ;
244
Abacus 25.3 Screens
if ( (Screen = OpenScreen (SNewScreen) ) == NULL)
exit (FALSE) ;
NewWindow. Screen = Screen; /* Do not forget! */
if ( (Window = OpenWindow(SNewWindow) ) = NULL)
exit (FALSE) ;
/* Wait for Close-Gadget */
Wait (1 « Window->UserPort->mp_SigBit) ;
printf ("\nLast window values: %d/%d/%d/%d\n\n",
Window->Lef tEdge ,
Window->TopEdge ,
Window->Width ,
Window->Height ) ;
CloseWindow (Window) ; /* Close everything in sequence*/
CloseScreen (Screen) ;
CloseLibrary ( Intuit ionBase) ;
exit (TRUE) ;
}
Since C programmers are usually too lazy to type, structure initializa-
tion is best performed during the definition of the variables. Another
innovation is the entry of CLOSEWINDOW in IDCMPFlags. In com-
bination with the new WINDOWCLOSE in Flags, the close gadget can
be tested. The Wait statement tells the system to wait for the activities
entered in the IDCMPFlags:
Wait (1 « Window->UserPort->n5>_SigBit) ;
Clicking the close gadget is the only way out. As in the window
program, all flags are set, which permit the user to change the size and
position of the window. The window pointer points to the desired
elements Lef tEdge, TopEdge, Width and Height.
Although the example program above uses three bit-planes, the
maximum accessible colors is eight. Therefore, the color registers can
be from to 7. Experimenting with screens takes up a lot of memory.
The program above requires almost 80K of RAM.
245
25. System Programming Amiga C for Beginners
2 5.4 Text/Graphic Window Display
Intuition sees little difference between processing text or graphics.
Since a printf call doesn't work in Intuition windows, something
else must be used.
25.4.1 Text
The Text function handles string output. A pointer to a RastPort
structure passes the text to the window structure. The user doesn't have
to know die appearance of RastPort or what function it performs. It
is enough to pass the expression to the responsible routine:
Window->FPort
Text requires a character string and its length as additional parameters.
The format is as follows:
Text (Window->RPort, string, length);
25.4.2 Move
The string passed by text appears at the current cursor position. The
Move function sets this position using this syntax:
Move (Window->RPort, xpos, ypos) ;
Before each call of the Text function, Move should position the
cursor. A small routine for this task follows:
text (w_ptr, s, x, y)
struct Window *w_ptr;
char *s;
int x, y;
{
Move(w_ptr->RPort, x, y) ;
Text (w_ptr->RPort, s, strlen(s));
}
246
Abacus 25.4 Text/Graphic Window Display
To keep the function generic, the pointer to the window in which the
text should appear is passed. Because of this you can service several
windows with the same function. A call appears as follows:
text (Window, "Attention!", 20, 40);
The text appears at position (20/40), if the window will allow it (the if
is important). You can write as much text as you wish in the window.
Intuition ensures that no window or screen is overwritten. If the text
can't be displayed completely in the window, the writing stops at the
window's right border. The user can be assured that nothing is
accidentally drawn in other windows.
25.4.3 Draw
The Draw function draws lines. The parameters of the routine are:
Draw(Window->PPort, x, y) ;
Something's missing here — you need two points to draw a line. With
Draw', the straight line is drawn between the current position and the
(x/y) point. The Draw function belongs to the graphics.library
instead of intuition.library. First this library must be opened,
then it returns a special pointer.
For drawing, the mouse coordinates are normally needed. They are found
in mouseX and mouseY which are two elements of the window
structure. This includes everything needed to write into a window.
In the following program argv and argc reappear. These other values
can be used from the CLI rather than the preset values. The call has the
following format:
prg X-RES Y-RES BITPLftNES
for example:
draw 640 200 3
It is interesting here that the resolution of a screen can be larger than
the maximum resolution of the display monitor. 640*200 pixels (640*
256 in PAL systems) can be represented, but if 800 dots are selected in
the horizontal axis, the window can be shifted beyond the right screen
border. The same is true of the vertical axis.
247
25. System Programming Amiga C for Beginners
25.4.4 Small Drawing Program
/* draw.c 25.4.3 */
/* From Amiga C for Beginners */
/* by Abacus */
♦include <exec /types. h>
♦include <intuition/intuition.h>
extern LONG OpenLibraryO ;
extern struct Screen *OpenScreen() ;
extern struct Window *OpenWindow{);
struct IntuitionBase *IntuitionBase;
struct GfxBase *GfxBase;
♦define INTUITION_REV
♦define GRAPHICS_REV
struct TextAttr Font =
{
"topaz. font",
TOPAZ_SIXTY,
FS_NORMAL,
FPF_ROMFONT,
};
UBYTE screentitle[81];
struct NewScreen NewScreen =
{
0,0,
640, /* Width */
200, /* Height; PAL version-may change 200 to 256 */
2, /* 3 bitplanes = 8 colors */
2,3, /* another color combination */
HIRES,
CUSTOMSCREEN,
SFont,
screentitle,
NULL,
NULL,
};
struct NewWindow NewWindow =
{
20, 20, /* X and Y Position */
400, 180, /* Width, Height */
0,1, /* Colors (0 - 7) */
CLOSEWINDOW,
WINDOWCLOSE | SMART REFRESH | ACTIVATE | WINDCWSIZING |
248
Abacus 25.4 Text/Graphic Window Display
SIZEBRIGHT | WINDOWDRAG | WINDOWDEPTH,
NOLL,
NOLL,
"* My window *",
NOLL,
NOLL,
190, 20,
640, 200, /* in PAL systems may change 200 to 256 */
COSTOMSCREEN
};
main (argc, argv)
int argc;
char *argv[] ;
{
struct Screen *Screen;
struct Window *Window;
register char s[81];
int color = 4;
register int x, y, xalt, yalt;
if ( (IntuitionBase = (struct IntuitionBase *)
OpenLibrary ("intuition . library" , INTOITION_REV) )
= NOLL)
exit (FALSE) ;
if ((GfxBase = (struct GfxBase *)
OpenLibrary ("graphics . library", GRAPHICS_REV) )
= NOLL)
exit (FALSE) ;
if (argc != 4)
{
printf ("Error in argumentsW) ;
printf ("X-Res Y-Res Bitplanes\n") ;
)
else
{
NewScreen . Width = atoi (argv [ 1 J ) ;
NewScreen . Height = atoi (argv [ 2 ] ) ;
NewScreen . Depth = atoi (argv [ 3 ] ) ;
if (NewScreen. Depth > 4 | | NewScreen . Depth < 1)
NewScreen . Depth = 2;
color = 1 « NewScreen . Depth;
NewScreen. DetailPen = color - 1;
NewScreen. BlockPen = color - 2;
sprintf (screentitle, "This screen has %d colors",
color) ;
if ( (Screen = OpenScreen (SNewScreen) ) — NOLL)
exit (FALSE) ;
249
25. System Programming Amiga C for Beginners
NewWindow . Screen = Screen; /* Do not forget! */
if (argc «= 4)
{
NewWindow. Width = Screen->Width/2;
NewWindow. Height = Screen->Height/3;
NewWindow. MinWidth = Screen->Width/3;
NewWindow . MinHeight = Screen->Height/5;
NewWindow. MaxWidth = Screen->Width;
NewWindow. MaxHeight = Screen->Height;
}
if ( (Window = OpenWindow(SNewWindow) ) == NOLL)
exit (FALSE) ;
text (Window, "Hello there ! " , 20, 20) ;
/* Initialize with start values */
Move (Window->RPort, xalt = Window->MouseX,
yalt = Window->MouseY) ;
/* Drawing starts here until upper or */
/* left border is reached */
while ( (x = Window->MouseX) > &&
(y = Window->MouseY) > 0)
{
sprintf(s,"X = %3d, Y =%3d", x , y) ;
text (Window, s, 150, 7);
Move(Window->RPort, xalt, yalt);
Draw(Window->RPort, xalt = x, yalt = y) ;
}
text (Window, "Please click the close gadget", 20, 20);
/* Wait for Close-Gadget */
Wait (1 « Window->UserPort->n5>_SigBit) ;
CloseWindow (Window) ;
/* Close everything in sequence*/
CloseScreen (Screen) ;
CloseLibrary (GfxBase) ;
CloseLibrary(IntuitionBase) ;
exit (TRUE) ;
}
text (wjptr, s, x, y)
struct Window *w_ptr;
char *s;
int x, y;
{
Move (w_ptr->RPort, x, y) ;
Text (w_ptr->RPort , s , strlen ( s ) ) ;
)
250
Abacus 25.4 Text/Graphic Window Display
Notice the new structure TextAttr with the variable Font. Every
NewScreen structure has, among other things, a component named
Font. Here the character set to be used can be stored (address of the
structure). Of course this is again a pointer to another structure,
TextAttr.
The structure for the definition of a character set is very simple. First
there is the name of the font, then the height of the character and the
manner of presentation. Finally a flag marks the location of the charac-
ter set. We used the character set built into ROM. This font is used in
the 60 character screen setting. It's somewhat larger than the 80
character version. Eighty characters can be displayed if you use
topaz_eighty instead of TOPAZ_SIXTY.
All entries of NewWindow and NewScreen are already initialized, but
if the user wants to use other values for resolution and bit-planes, they
can be accepted. The maximum and minimum size of the windows
must also be adjusted. Since the color indices of the window are always
ready for use with and 1, no conversion has to be performed. The
screen, on the other hand, gets the last two color registers which of
course depend on the number of colors. The program permits a maxi-
mum of 16 colors, which equals four bit-planes, in the high resolution
mode. The tide of the screen displays this information. For this reason
an additional variable must be used because the structure has made no
provisions for storing the tide.
As soon as the window is opened, the text appears. The mouse can be
used to draw something. As long as the mouse pointer doesn't move
beyond the upper or left border of the window, a line will be drawn. The
mouse position is always indicated in the tide line. This is not
absolute, but relative to the upper left corner of the window. For this
reason a negative value is possible when the mouse is pushed beyond
the left or upper border. The program uses this as an end criterion.
Because of the output of the mouse coordinates, the current character
position in xalt and yalt must be stored in intermediate storage.
Before the drawing of the line, the values are restored again with the
Move function. We have said enough about this program.
However, we have some additional suggestions. Up to now only the
define hires was used for user defined screens in viewModes, which
achieves a horizontal resolution of up to 640 pixels. The Amiga can
also produce a lower resolution which fills a complete display line with
320 pixels. With the same number of colors, only half the memory
space is required. The possibility of working with five bit-planes and,
therefore, 32 different colors is created. The only thing required for this
is to replace HIRES with null. Try this on the first screen program.
Besides the change mentioned above, only the width of the screen must
be set to the 320 pixels. If five bit-planes were requested, 32 colors are
available in color registers 0-31.
251
25. System Programming Amiga C for Beginners
25.4.5 Low Resolution and Interlace Modes
The interlace mode can be switched on in viewModes. The display
gets a vertical resolution of 400 (PAL systems — 512) instead of 200
(PAL— 256) pixels. Not bad, but here comes the big "but!" This
process can only be realized by lowering the refresh frequency of the
monitor from 50 to 25 Hz. A flickering image occurs on the Amiga
monitor. This mode was only intended for those monitors which had a
long screen refresh rate and thereby don't create flickering. Examine the
display and form your own judgment. The define LACE in the
ViewModes enters interlace mode. Some examples:
Low resolution (320 pixels):
NewScreen. ViewModes ■= NULL;
High resolution (640 pixels) and interlace (400 pixels):
NewScreen .ViewMode = HIRES | LACE;
Low resolution (320 pixels) and interlace (400 pixels):
NewScreen. ViewModes = LACE;
With 32 colors, a function which permits changing the color of the pen
would be useful. This input changes the current color in the color regis-
ter
SetAPen (Window->RPort, color) ;
To see this routine in action, a new program must be written. Add the
following lines to the drawing program. First, at the beginning of the
main function, add the definition of a variable named colour:
register int x, y, xalt, yalt, colour = 1;
At the end of the while loop add two additional lines. Here is the
complete loop :
while ( (x = Window->mouseX) > &&
(y = Window->nvouseY) > 0)
{
sprintf (s, "X =%3d, Y = %3d, x, y) ;
text (Window, s, 150, 7) ;
Move(Window->RPort, xalt, yalt);
Draw(Window->RPort, xalt = x, yalt - y) ;
SetAPen (Window->RPort, colour++) ; /* New! */
if (colour = color) colour = 1; /* New! */
}
252
Abacus 25.4 Text/Graphic Window Display
This program is on the optional disk as drawl 6.c. In the beginning
the variable colour is set at 1 to draw with the first color index (0 is
the background color). After each small line fragment, the pen color
changes until the last index (number of colors- 1) has been reached. Then
it starts over. This produces all the colors for the first run, including the
registers not normally used. To make it even more colorful than the 16
colors in the HIRES mode, change the safety test:
old: if (NewScreen. Depth > 4 | | NewScreen. Depth < 1)
NewScreen . Depth = 2;
to
new: if (NewScreen. Depth > 5 | | NewScreen. Depth < 1)
NewScreen. Depth = 2;
and change the HIRES to null. Consider the reduced X resolution of
320 pixels instead of 640 pixels and change the program accordingly.
This permits drawing with 32 colors in one window. This program is
on the optional disk as draw32.c. An example call of the program for
32 colors:
draw32 320 200 5
Since many colors and high resolution require a large amount of mem-
ory, here are some examples of memory usage by windows and screens.
Low resolution, interlace mode, 32 colors:
320 (pixels) * 400 (pixels) * 5 (bitplanes) / 8 (bits per
byte) = 80,000 bytes = 78K (PAL 320*512*5/8 = 102,400)
High resolution, interlace mode, 8 colors:
. 640 (pixels) * 400 (pixels) * 3 (bitplanes) / 8 (bits per
byte) = 96,000 bytes = 93K (PAL 640*512*3/8 = 122,880)
Low resolution, 2 colors
320 (pixels) * 200 (pixels) * 1 (bitplanes) / 8 (bits per
byte) = 8,000 bytes = 7.8K (PAL 320*256*1/8 = 10,240)
25.4.6 Pixel Processing
Other graphic commands besides Draw are:
ReadPixel (Window->RPort, x, y) ;
WritePixel (Window->RPort, x, y) ;
253
25. System Programming Amiga C for Beginners
ReadPixel ReadPixel tests whether the indicated position of apixel was set and
returns the color value of the pixel. If no pixel was visible, because the
pixel has the same color as the background, ReadPixel returns a to
the register number. If the pixel is outside the window whose port is
passed, the result is -1.
WritePixel WritePixel sets a single pixel at the position indicated. The color
used depends on the current color as in all other routines and is deter-
mined by SetAPen.
The following is a program which changes the title line of the window
used in a sine format
/* pixel. c 25.4.6 */
/* From Amiga C for Beginners */
/* by Abacus */
♦include <exec /types. h>
♦include <intuition/intuition.h>
extern struct Window *OpenWindow() ; /* Declaration */
extern long *ppenLibrary () ; /* Hello Aztec-User! */
extern double sin();
struct IntuitionBase *IntuitionBase;
struct GfxBase *GfxBase;
♦define INTUITION_REV
♦define GRAPHICS_REV
/* Number of colors of Workbench */
♦define WB_COLORS 4
struct NewWindow NewWindow =
{
10, 50, /* X and Y Position */
360, 120, /* Width, Height */
3, 2, /* Color Indexes */
NULL,
SMART_REFRESH | ACTIVATE | WINDOWDRAG | WINDCWDEPTH,
NULL,
NULL,
"This Line is changed!",
NULL,
NULL,
0, 0,
640, 200, /* PAL users - change 200 to 256 */
WBENCHSCREEN
};
main ()
{
struct Window *Window;
register struct RastPort *r;
254
Abacus
25.4 Text/Graphic Window Display
register int i, j, top, yoffset;
int i_to, j_to, color, colors [512];
double factor;
if ( (IntuitionBase = (struct IntuitionBase *)
CpenLibrary ( "intuition . library" , INTUITIONJSEV) )
= NOLL)
exit (FALSE) ;
if ((GfxBase = (struct GfxBase *)
QpenLibrary ("graphics. library", GRAPHICSJREV) )
«=• NOLL)
exit (FALSE) ;
if ((Window = QpenWindow(SNewWindow) ) = NOLL)
exit (FALSE);
r = Window->RPort;
top = Window->Height / 4;
factor = 2 * 3.1415926 / Window->Width * 1.5;
/* 1.5 Sine Waves */
for(i = 2, i to = Window->Width - 2; i < i_to; i++)
{
for(j =0; j < top; j++) /* A vertical line */
{ /* Transfer to Array */
color = ReadPixel(r, i, j);
if (++color = WB_COLORS)
colors [j] = 0;
else
colors [j] = color;
/* increase color index by one */
}
for(j = 0,
yoffset = top + top * sin (factor * i) + 16;
j < top; j++)
if (colors [j]) /* If Pixel should be set */
{
}
SetAPen (r, colors [ j ] ) ;
WritePixel (r, i, j + yoffset) ;
}
Delay (1500); /* Wait 1500 Ticks = 30 seconds */
CloseWindow (Window) ;
CloseLibrary (GfxBase) ;
CloseLibrary (IntuitionBase) ;
exit (TROE) ;
}
Lattice
The library for mathematical functions and floating point numbers must
be linked with the standard library. Example:
lc -Lm math2
255
25. System Programming Amiga C for Beginners
Aztec If you work with the Aztec compiler, the library for mathematical func-
tions and floating point numbers must be linked with the standard
library c.lib. Example:
cc +L math2.c
In math2.o -lm -lo
How the The program runs under the Workbench screen and uses its colors. Two
program bit-planes (four colors) are the default If the user constructed a Work-
works: bench which deviates from this, the define wb_colors must be
adjusted accordingly. The window which was defined in the NewWin-
dow structure contains only front and back gadgets. The size cannot be
changed.
In a large loop which processes the complete width of the window, all
pixels belonging to one X position are gathered in one array. Before the
value which is returned from the ReadPixel is stored, a color trans-
formation is made. Every pixel gets the color from the following regis-
ter. The area of the display which is transmitted, is the upper quarter of
the window. To prevent mix-ups between the information to be read and
written, a complete column is first saved into the array colors. Then
the new position of the pixels is calculated using the sin (sine) func-
tion. The dots are written in the new color with WritePixel at the
new position. The pixels which are the same color as the background
are taken out This is tested first to increase the speed. The program
will display the top line as a sine wave.
After complete transformation, the Delay function slightly delays the
end of the program to give the user the opportunity to view the window
again. The parameter provides the waiting time in 1/50 second ticks. To
achieve a delay of 30 seconds 1,500 ticks must be stored.
256
Abacus 25.5 DOS
25.5 DOS
Besides Intuition, DOS (the Disk Operating System) is usually required
when programming. Many programs wouldn't work without the help of
AmigaDOS. The DOS routines handle file deletion and renaming, as
well as directory creation and directory display.
DOS is also stored in a library file (do s. library). Unlike the other
libraries, dos. library is always open to the user. It doesn't have to
be opened or closed by the user. It is as simple to use as the functions
from the standard library. For example, deleting a file:
result = DeleteFile (filename) ;
The return value is an integer number which indicates an error if zero
and the correct processing with a number unequal to zero. Complete
directories can be deleted with this function. No files may be contained
in the directory. They must be erased in advance. The Rename function
is just as easy to use for renaming files:
result = Rename (old_name, new_name) ;
The result is also a value unequal to zero. The other parameters
old_name and new_name are just like the filename strings which
contain a valid filename.
257
25. System Programming Amiga C for Beginners
25.6 SetComment
One routine permits the attachment of a comment to a file. This com-
ment is completely independent of the content and size of the file and is
stored in the same place as the filename and its parameters. The DOS
command filenote in the C: directory can attach a comment text to
an existing file. This can also be done with the function:
result = SetComment (filename, comment) ;
A short program shows this routine in action:
/* makecom. c 25.6 */
/* From Amiga C for Beginners */
/* by Abacus */
finclude <libraries/dos.h>
main(argc, argv)
int argc;
char *argv [ ] ;
{
if (argc == 3)
{
if ( ! SetComment (argv [ 1 ] , argv [2 ] ) )
printf ("Error %d\n", IoErrO);
)
else
printf ("Format: MAKECOM FILE COMMENT\n") ;
exit (TRUE) ;
}
The filename and the comment passes to the program through the
command line. As in all data transfers, the use of spaces in the actual
comment is not permitted. Here is a sample call:
makecom makecom. c This-is-a-comment-use-the-list-command-to-display-it
258
Abacus 25.7 Read Directory
2 5.7 Read Directory
Many programs that handle files should have a routine for reading disk
directories. To make this possible in a program, various functions are
required.
First there is the Lock function. Lock locks the specified directory for
access. Only after the Lock can other functions operate on the direc-
tory. The name of the directory and the access mode are passed to
Lock. Finally an integer value for read is passed with the define
ACCESS_READ. The returned key permits the processing of this one
directory, similar to a handle for file accesses or a window pointer under
Intuition. If this key is equal to zero, an error has occurred.
Two functions are required for reading a directory. One is Examine,
the other ExNext. First Examine must be called to obtain the first
entry of the directory. Then a call for ExNext must follow for each
additional file or directory. Both routines require both Lock and a
pointer to the Fileinf oBlock structure. This structure contains all
important file data.
result = Examine (lock, Sf ileinfo) ;
And here is the structure definition:
struct FilelnfoBlock {
LONG fib_DiskKey;
LONG fib_DirEntryType;
char fib_FileName[108];
LONG fib_Protection;
LONG fib_EntryType;
LONG fib_Size;
LONG fib_NumBlocks;
struct DateStamp fib_Date;
char fib_Comment[116];
}
The f ib_DirEntryType function indicates whether the data cur-
rently read is a normal file (<0) or a directory (>0).
The f ib_FileName function contains the name which can be up to
30 characters long, even though it was generously defined here as 108
characters.
The fin_Protection function contains flags which indicate
whether the file can be read, written, executed or erased. The variable is
defined as long (32 bits), but only the lower 4 bits are required.
259
25. System Programming Amiga C for Beginners
Hie priorities for these files are as follows:
R
W
E
D
8
4
2
1
= Read
W = Write
E => Execute
D = Delete
For every protective action one of the bits above must be set. For
example if a file or directory can only be read or erased, the flags W and
E must be set:
RWED
0110 (bits) =4+2=6
This variable must contain the value 6. It is important to set the flag
whose function is forbidden. To make changes please use the protect
command from the CLI. The flags which are passed with this program
are changed in such a manner that the functions can be performed. This
is exactly the opposite of their use in the user program. To protect a
file from erasing, the following line is required:
PROTECT ED RWE
The f ib_Si ze function defines the file size in bytes.
The f ib_NumBlocks function contains the number of occupied
blocks on the disk.
The f ib_Date function contains the date when the file was last
written.
The f ib_Comment function contains the comments for the file.
You now have all the information needed to construct the final pro-
gram. For the sake of simplicity we use parameter passing with the
command line in this version. This parameter indicates the directory
which should be read.
/* read_dir.c 25.7 */
/* From Amiga C for Beginners */
/* by Abacus */
♦include <libraries/dos.h>
struct FilelnfoBlock fi;
main(argc, argv)
int argc;
char *argv [ ] ;
{
long lock;
int error;
char filepathflOO];
if (argc =2) /* parameter present ? */
260
Abacus 25.7 Read Directory
strcpy (f ilepath, argv [1 ] ) ;
else
strcpy (f ilepath, "sys : " ) ;
lock = Lock (f ilepath, ACCESS_READ) ;
printf ("Lock value %d\n", lock);
if (! lock)
{
printf ("No Lock! ERROR! \n");
exit (FALSE) ;
)
if (Examine (lock, &f i) ) /* First call successful? */
do
output (); /* Return value not of interest now */
while (ExNext (lock, Sfi)); /* until error occurs */
error = IoErr(); ■/* What Error? */
if (error != ERR0R_N0_M0RE_ENTRIES) /* "real" Error! */
printf ("Error %d occurred! \n", error);
exit (TRUE) ;
}
output ()
{
if (!*fi.fib_FileName) /* strlen = */
{
printf ("Empty ! \n" ) ;
/* for example Root-directory of RAM Disk */
return (0); /* That's directory without name */
}
if (fi.fib_DirEntryType > 0)
printf ("Directory name") ;
else
printf ("Filename ") ;
printf (": >%20s< RWXD %lx bytes: %-61d Blocks %-41d\n",
f i . f ib_FileName , f i . f ib_Protection ,
f i . f ibJSize , f i . f ib_NumBlocks ) ;
if (*fi.fib_Comment) /* If comment present, output! */
printf ("Comment: >%s<\n", f i . f ib_Comment) ;
return (fi . fib_DirEntryType > 0); /*Return File Type */
}
The protect flags are not decoded separately in this program (it wouldn't
be a problem to do that), but are presented as a hexadecimal number (the
"%lx" format instruction). You can enhance this program if you wish.
The flags can be displayed in RWED format using the LIST command
from the CLI. With protect any flag can be set and with LIST the
result can be observed. This information can be compared with the
results from the user program.
261
25. System Programming Amiga C for Beginners
25.8 Conclusion
You now have the general knowledge needed to write simple programs
in C language. As you take time to develop your own programs,
functions and libraries, keep this book nearby for reference. Since it's
difficult to memorize everything about a language, this book will help
you with the complex concepts of C language.
You may be wondering why we didn't spend more time with some
aspects of the Amiga. We admit that we didn't include as much about
the operating system and Intuition as we would have liked. However,
these are difficult concepts for a beginner to understand, and we felt it
best to just give the reader a few general examples controlling these
areas in C. Since C is a transportable language, you may prefer to write
transportable source codes.
If you want to continue your education in C, we recommend the Abacus
book Amiga C for Advanced Programmers. This book covers subjects
that interest professional Amiga programmers: Combining assembly
language and source codes; debugging (finding errors); jump tables; and
more. In addition, Amiga C for Advanced Programmers details
Intuition programming in C (menus, requesters, etc.).
We wish you luck in your future as a C programmer.
Dirk Schaun
262
Appendices
Abacus Appendix A: Functions
A. Functions
Filename: strlen . c
/*******************************************************/
/* Name: strlen */
/* Parameter: s (String) */
/* Return value: Length (int) */
/* Function: Number of characters in "s" */
/* Other: - */
./♦A*****************************************************/
strlen (s)
char s [ ] ;
(
register int i = 0;
while (s [i] )
i++;
return (i) ;
>
Filename: strcpy . c
/♦♦♦♦it************************************* *************/
/* Name: strcpy */
/* Parameter: s (String), t (String) */
/* Return value: - */
/* Function: Copies "s" to "t" */
/* Other: - */
/************************************************ *******/
strcpy (t,s)
register char *t,*s;
{
while (*t++ = *s++)
r
)
Filename: strcat . c
/•••••♦A**********************************************/
/* Name:. strcat */
/* Parameter: s (String), t (String) */
/* Return value: - */
/* Function: attach "t" to "s" */
/* Other: - */
/A****************************************************/
strcat (s,t)
265
Appendix A: Functions Amiga C for Beginners
register char *s,*t;
{
while (*s)
s++;
while (*s++ - *t++) ;
)
Filename: letter . c
/A*****************************************************/
/* Name: letter */
/* Parameter: z (char) */
/* Return value: It was a letter (1), else (0) */
/* Function: Determines if it was a letter or not */
/* Other: - */
/A*****************************************************/
♦define FALSE
#define TRUE 1
letter (z)
register char z;
{
if ( (z >= 'a' ss z <= -'z') II (z >= 'A* && z <= 'Z') )
return (TRUE);
return (FALSE) ;
)
Filename: c_comp . c
/♦A*****************************************************/
/* Name: c_comp */
/* Parameter: cl (char), c2 (char) */
/* Return value: 1 (TRUE)', (FALSE) */
/* Function: Compares two characters */
/* Other: requires two characters () */
/••a****************************************************/
♦define FALSE
♦define TRUE 1
extern int grklflag;
c_comp(cl,c2)
register char cl,c2;
{
if (cl == c2) return (TRUE) ;
if( grklflag && letter (cl) SS letter (c2) )
if ( (cl + "a" - 'A' == c2) I | (c2 + "a" - 'A' == cl) )
return (TRUE) ;
return (FALSE) ;
)
266
Abacus Appendix A: Functions
Filename: strcmp . c
/♦it**************************************************/
/* Name: strcmp */
/* Parameter: s (String), t (String) */
/* Return value: identical not identical 1 */
/* Function: Compares "s" and "t" */
/* Other: - */
/•••••••A*********************************************/
strcmp(s, t)
register char *s, *t;
{
register int identical;
while (identical = c_comp(*s, *t++) )
if (!*s++)
return (0) ;
return ( ! identical) ;
)
Filename: strchar.c
/A******************************************************/
/* Name: strchar */
/* Parameter: s (String), c (char) */
/* Return value: Position (int), or -1 */
/* Function: Determines Pos of the Char "c" in "s"*/
/* Other: - */
/•••A***************************************************/
strchar (s,c)
register char s [ ] ;
register char c;
(
register int i = 0;
while ( !c_comp(s [i] ,c) ss s[i])
i++;
if(s[i]) return (i);
return (-1) ;
}
Filename: strchbac . c
/******************************************************/
I* Name: strchback */
/* Parameter: s (String), c (char) */
/* Return value: Index (int) */
/* Function: Searches for Pos of Char "c" in "s" */
/* Other: requires c_comp(), strlenO */
/************************************************** ****/
strchback (s,c)
register char s [ ] ;
267
Appendix A: Functions Amiga C for Beginners
register char c;
<
register int i = strlen(s);
while ( (i >= 0) && !c_comp(s [i] , c) )
i — ;
return (i); /* Error = -1 */
)
Filename: ilatoila . c
/*******************************************************/
/* Name: ltoa */
/* Parameter: n (long), s (String) */
/* Return value: - */
/* Function: Converts long value to char string */
/* Other: requires reverse () */
/•♦•a***************************************************/
tdefine TRUE 1
tdefine EOS ■ \0'
ltoa(n, s)
register char s [ ] ;
register long n;
{
register int i = 0;
register int forechar = 0;
if (n < 0)
{
forechar = TRUE;
n = -n;
}
do
{
s [i++l - n % 10 + '0' ;
) while ((n /= 10) > 0) ;
if (forechar )
s[i++] = '-';
s[i] = EOS;
reverse (s) ;
/•A*****************************************************/
/* Name: itoa */
/* Parameter: n (int), s (String) */
/* Return value: - */
/* Function: Converts integer number to char string */
/* Other: requires ltoat) */
/***************************************************** */
itoa(n, s)
register int n;
register char s [ ] ;
<
ltoa( (long) (n) , s) ;
268
Abacus Appendix A: Functions
/it******************************************************/
I* Name: atol */
/* Parameter: s (String) */
/* Return value: n (long) */
/* Function: Converts char string into long value */
/* Other: - */
/*******************************************************/
long atol(s)
register char *s;
{
register long val;
register int sign = 1;
while (*s == ' ')
s++;
if (*s == '+' | | *s == '-')
sign = (*s++ == ■+■) ? 1 : -1;
for (val = 0; *s >= '0' && *s <= ■ 9"; ++s)
val = 10 * val + *s - ' 0';
return (sign * val);
}
/a******************************************************/
/* Name: atoi */
/* Parameter: s (String) */
/* Return value: Integer number */
/* Function: Converts Char string into Integer */
/* Other: - */
/A******************************************************/
atoi (s)
register char *s;
(
long atol () ;
return (atol (s) ) ;
)
269
Appendix B: The History of C Amiga C for Beginners
B . The History of C
C originated from BCPL (Basic Cambridge Programming Language).
The B language came from BCPL and C came from the B language. C
was developed in the mid-seventies by Dennis M. Ritchie, who, at that
time, was working for Bell Laboratories.
C was originally intended for developing an operating system which,
among other things, would be capable of multi-user and multitasking
execution, namely UNIX. This explains why C programs are so fast.
Multitasking procedures require a very fast operating system which up
to then could only be written in assembly language. Dennis Ritchie
developed the C language to circumvent the error prone and unclear
assembly language programming. The result, the UNIX operating
system, consists of about 13,000 lines of which only a minimum of
about 800 lines were written in assembly language. The rest of the
operating system is in C.
C became popular with the introduction of the Amiga and the Atari ST,
whose operating systems were written in C. The Amiga's Intuition user
interface was written almost completely in C. Professional program-
mers and software houses prefer using C to develop new programming
projects. C has another advantage: it is portable. This means that C
programs can, theoretically, be transferred to other computers and
compiled there without changes.
The reason for this is that C has a small number of commands available
to all compilers. Parts which are computer specific, such as input and
output, don't belong to the actual C language. These routines are
delivered with the language in libraries adapted to the peculiarities of the
particular computer. The C programmer doesn't have to be concerned
about this. He knows that the getchar function gets a character from
the key-board, regardless of whether the program is executing on a C64,
an IBM PC, an Amiga or an Atari ST. This portability means less
programming for the developers — just transfer the program over to
another computer, make the changes needed for the new computer and
recompile it.
How a C Every C compiler has been split into various program portions which,
compiler depending on the manufacturer, are available either in a program module
works or in several smaller programs.
The first part of a C compiler is the preprocessor; this only replaces one
text portion with another according to the user's commands. The result
of this effort is a file containing pure text which can be processed with
the editor. This result passes to the scanner which searches for com-
mand words specific to C. It recognizes these words and stores them in
270
Abacus Appendix B: The History of C
abbreviated form. In this format the command is stored as a token (code)
instead of as individual letters. Tokenizing takes up less memory and
accelerates the translation.
Parser After completing this test run, the parser appears. It tests the source
code commands for correct syntax, and differentiates between correct and
incorrect combinations of C commands. The parser knows all the rules
about C syntax. Just as in everyday conversation, stringing words
together isn't enough. The parser ensures that the expression is correct.
As the last part of the actual C compiler, the code generator converts
the text processed by the parser into machine language commands.
Some C compilers first translate the machine language commands into
assembly language so the programmer can streamline the generated
code. This is really unnecessary since the C compilers on the market
already produce very efficient machine language code. After completing
this run, the compiler saves the object file to disk with the extension of
.o.
The final process is linking the object files with the required libraries to
produce an executable program. The linker is used for this purpose.
271
Appkndix C: The Lattice C Compiler Amiga C for Beginners
C . The Lattice C Compiler
C compiler manufacturers are constantly updating and improving their
compilers. For instruction on how to install the compiler, see the
documentation and any readme files that came with the compiler.
The C The C compiler is called with lc and the source filename. As a mini-
compiler mum the following is required:
lc hello
With the -L option, the linker can be loaded immediately after the call
of the C compiler. The linker (here BLINK) can also be called indepen-
dently. This is a standard call to compile and link a source code named
math2.c into a program named math2.
When the library for mathematical functions and floating point numbers
must be linked with the standard library, the following can be used:
lc -Lra math2
The linker The program BLINK provides a powerful linker for the programmer.
Here are the most important options available in this linker:
After the name BLINK all files which are linked together appear after
the FROM argument (or ROOT, or even nothing) . The name of the pro-
gram to be executed follows the TO argument. Library files to be
searched are listed after the library argument. Some sample calls:
BLINK FROM a,b,c TO program
BLINK a+b+c TO program LIBRARY folder/d
BLINK ROOT a,b,c TO folder /prg LIBRARY
system/lib, ob j/special
Using the parameter WITH all options can be stored in a file just as in a
MAKE file. A linker call is then:
BLINK WITH file
In this file the options mentioned above contain a parameter in each
new line. Example:
ROOT a , b , c
TO folder/prg
LIBRARY system/lib, ob j/special
272
Abacus Appendix D: The Aztec C Compiler
D. The Aztec C Compiler
C compiler manufacturers are constantly updating and improving their
compilers. See the documentation that came with the compiler for
instruction on how to install the compiler. Be sure to read any README
files.
The compiler The compiler with the name CC can be found in directory C:. The call
is very simple:
cc file.c
The source file file.c is compiled and translated into assembly code.
This code can be optimized by a machine language programmer. This
file has the name ctmpAXX.Xxx, where x is a number which differs
from one call to the next. It is best to look at the current directory
because this name is needed immediately.
Also Aztec uses symbolic names for devices which are listed as
follows:
CLIB
INCLUDE
CCTEMP
CCTEMP determines where temporary files created by the C compiler
will be stored. CLIB indicates the path to the libraries, while
include is the path for the header ( . h) files. Examples are:
assign CLIB: dfO:lib/
assign INCLUDE: dfO : include/
assign CCTEMP: ram:
Various options can be placed in front of the name of the file to be
compiled. Here are the most important:
-Ipath:
With -la pathname can be provided in which the Include files
are assumed to be. The search for these files is made only in this
sub-directory. The option is comparable with the assignment
INCLUDE (see above).
Note : The pathname immediately follows the I without any additional spaces.
For example:
cc -Iram.-includes/privat/
273
Appendix D: The Aztec C Compiler Amiga C for Beginners
+C creates longer code, since jumps within the program code arc
equipped with 32-bit commands instead of the 16-bil commands
which could have been used.
+D causes data to be stored in 32-bit format. This slows down data
access and increases memory requirements, but makes data
segments of any desired size possible (theoretically). During a
"normal" data access with 16-bit addressing, the user is limited to
a maximum of 64K of data.
+L Variables and constants of int type arc stored in 32-bit format.
Because of this the programs become (partially) Lattice compati-
ble since this compiler always uses 32 bits. Without this option
16 bits arc sufficient for int numbers.
-D defines a constant. It corresponds to the # define statement,
but is assigned during the call of the compiler. No space can
follow this option character. Example:
cc -DTESTRUN--1 f ilo.c
The assignment corresponds to the define .
« define TESTRUN 1
-S suppresses "warnings." The warnings arc only messages and the
compiled programs arc usually capable of being run. To identify
the real errors, this option can be used to display only the error
messages on the monitor.
+p causes the compiler to create Lattice compatible code. All data,
jumps and int numbers arc automatically created in the 32-bit
version.
The assembler After the C compiler comes the assembler which is named AS. It is
also stored in the C: directory. The call is similar to the C compiler:
as file.o
With the option -o a new name can be given to the new file. Example:
as -0 program. o ctmpxyz.123
Additional options arc only of interest to the assembler specialist. Since
this book deals with C programming, they will not be considered
further. It is only an intermediate step.
The linker For Aztec the linker provided is called In and can be found in the C:
sub-directory. The files to be linked together arc placed one behind the
other. Whether they arc libraries or modules doesn't matter in principle,
but libraries should be placed at the end of the list.
274
Abacus Appendix D: The Aztec C Compiler
In file.o c.lib
The standard file c.lib is also like all other libraries in the lib :
directory. Several modules can be linked together
In -o result moduli. o modul2.o modul3.o c.lib
The name assignment for the resulting program is performed with -O.
The linker can be informed about libraries with -L, but the extension
of .lib is then omitted. Example:
In file.o -Lc -Lm
Two additional options are +C and +F which permit selection of special
storage areas. A code letter follows the option which has the following
significance:
c Program
d Initialized data
b Data which was not initialized
The +C stands for chip memory, +F for fast memory. These two
groups of RAM areas are especially important for graphic programming
since certain data must always be stored in the chip-memory. With this
option the following can be requested:
In +Cdb +Fc file.o -Lc
This causes the storage of data in chip-memory and the storage of the
program in the normal fast memory. Without a special statement, all
information would have been stored in the fast memory area.
Here is a make file which is tailored to Aztec C.
.key file
echo " Compiling <file$tl>.c "
cc -t <file$tl>.c
echo " Assembling <f ile$tl>.asm "
as <f ile$tl>.asm
echo " Linking <f ile$tl>.asm to <file$tl> "
In <file$tl>.o -lm -lc
; -lm -lc is called :link clib and mathlib in addition
echo " Everything clear ! "
The file is named a z -make on the optional program disk. Here is an
example call to compile, assemble and link a source file named
array.c:
execute az-make array
275
Appendix E: Reserved C Words
Amiga C for Beginners
E.
Reserved C Words
Commands which are presented here, but were not described in the
book, either have no function in the current C compilers, or are reserved
for future versions.
auto
enum
short
break
extern
sizeof
case
float
static
char
for
struct
continue
goto
switch
default
if
typedef
do
int
union
double
long
unsigned
else
register
void
entry
return
while
276
Abacus
Appendix F: C Operator Precedence
F. Operator Precedence
Precedence Onerator
Description
Evaluation
1
Function
left to right
[]
Array
left to right
Structure declaration
left to right
->
Structure declaration (pointer)
left to right
2
cast
Forced type conversion
right to left
*
Content of
right to left
&
Address of
right to left
-
Negative sign
right to left
i
Logical NOT
right to left
~
Bitwise complement
right to left
++
Increment
right to left
—
Decrement
right to left
sizeof
Storage requirement
right to left
3
*
Multiplication
left to right
/
Division
left to right
%
Remainder (modulo)
left to right
4
+
Addition
left to right
-
Subtraction
left to right
5
>
Shift to right
left to right
<
Shift to left
left to right
6
<
Less than
left to right
>
Greater than
left to right
<=
Less than or equal to
left to right
>=
Greater than or equal to
left to right
7
==
Equal
left to right
i =
Unequal
left to right
8
Bitwise AND
left to right
9
A
Bitwise EXOR
left to right
10
1
Bitwise OR
left to right
11
&&
Logical AND
left to right
12
1 1
Logical OR
left to right
13
•? :
Conditional evaluation
right to left
14
=
Assignment
right to left
#=
Abbreviated assignment
right to left
# from (+, -, *, /, %, », «
, &, 1, ~)
15
»
Separation of expressions
left to right
277
Appendix G: Storage Classes Amiga C for Beginners
G. Storage Classes
Storaee class
Validity
Duration
auto
Block
Block
extern
Program
Program
register
Block
Block
static (intern)
Block
Program
static (extern)
File
Program
H. Type Conversions
Rules:
1. char and short are always converted to int and float into
double.
2. If after this conversion one of the operators should have the type
double, the second operand and the result are also converted to
double.
3. If a data type is long, all participating values are also trans-
formed to long.
4. If an unsigned value is found among the operands, all values
are converted to unsigned.
278
Abacus
Appendix I: Modes for fopen
I.
Modes for fopen
Lattice C
String Create Cut file Read Write Append Binary
T
*V
"a"
"r+"
,s w+"
"a+"
"ra"
"wa"
"aa"
"ra+"
"wa+"
"aa+"
'Vb"
"ab"
"rb+"
"wb+"
"ab4-"
no
yes
yes
no
yes
yes
no
yes
yes
no
yes
yes
no
yes
yes
no
yes
yes
no
yes
no
no
no
no
no
yes
no
no
no
no
no
yes
no
no
no
no
yes
no
no
yes
no
yes
no
yes
no
no
yes
yes
yes
yes
no
yes
yes
yes
no
yes
yes
no
yes
yes
yes
no
no
no
no
yes
no
no
no
no
yes
no
yes
yes
no
no
yes
yes
no
no
yes
no
yes
no
yes
no
no
yes
no
yes
no
yes
no
no
yes
yes
yes
yes
no
yes
yes
yes
no
yes
yes
no
yes
yes
Changes for
Aztec
No conversions are made for binary files, If the file was opened as an
ASCII file, which can be recognized by the "a" at the second place, all
carriage returns (code 13 = \r) are eliminated and the character with the
ASCII code (26) is converted to EOF (-1) during reading. During writ-
ing, the single line feed (\n), is converted to the character combination
\r\n.
To differentiate the two modes, Lattice C uses an external int variable
named _fmode. If the highest value bit is set (_fmode & 0x8000),
the binary mode is used, or else the conversions indicated are performed.
Aztec opens all files in binary. Aztec also offers the "x" and "x+"
modes which open a file for writing. If the file doesn't yet exist, it is
created. With "x+" the file can be read and written after opening.
279
Index
? conditional operator
163
CPU
206
213
create
Abbreviations
34,95
<CtrlxX>
18
Activate
237
Addresses
131
Datatypes
105, 182, 231
AND
165
De-referencing
133
Arguments
28, 105, 203
Decimal notation
85
Arrays
115, 189
Declarations
99, 181
ASCII code
10,84
Decrement operator
97
auto
143, 155, 181
define
174, 206
Aztec C 19,39,41,47,65,210
Definition
99
Direct access
216
Backslash
29,85
Directives
229
<Backspace> key
18
do while loop
49,58
BASIC
4,48
DOS
257
Bit fields
175
double 67,
106, 136, 178
Bit manipulation
165
Bit shifting
167
ED
10,91
Bit-planes
251
Editor
3,9
Bitwise shift opperators
167
else
33
Braces
25,28
End of paragraph
27
break
123
enum
177
Buffer
206
EOF
209
Error checking
49
C language
4
Errors
189, 196, 231
Calculation
35,61
<Esc> key
18
case statement
189
Escape sequences
28
cast operator
71
EXCLUSIVE OR
168
char 39,
57,68,111,115,
extern 99,
, 100, 145, 181
133,136, 181, 203
char pointer
191
fgetc
211
Character strings
39
File extension
10
CLI 10, 13,
17, 25, 203, 228
File mode
208
Comments
30, 258
float 67,
, 115, 136, 146
Comparison operators
45
173, 181, 195
Compiler
3-5, 9, 27, 153
Floating point numbers
37
Complex data types
173
Floating point variables
67
CON
219
Flowchart
9
Conditional operator
163
fopen
207
Console
218
for
48, 57, 123
Constant
177
Format specification
32,77
continue
123, 125
f print f
211,220
Conversion program
82
fputc
211
281
Index
Amiga C for Beginners
fread 211
fscanf 208,211
fseek 216
ftell 217
Function 12, 25, 28, 82, 105, 143, 195
f write 211
Gadget
getc
getchar
Global variables
goto
Guru Meditation
Header files
Hexadecimal system
High level languages
Icons
if
Increment operator
Index
Initialization
235
206
148, 207, 218
155, 156
169
37
91, 206, 236
80,81
4
17, 227, 235
32-33,45,119
97
58
99, 184
irit 31, 67, 106, 115, 133, 181, 231
Integer division 61
Integer variables 31
Integers 31
Interlace 252
Interpreted languages 4, 5
Intuition 235, 238
itoa 157
main function
MAKE file
Menus
Modula2
Modules
modulo
Mouse
Multi-dimensional arrays
Multiple assignment
Multiple dimensions
Multitasking
Nocarerefresh
Number conversion
Object code
Octal system
One's complement
One-dimensional arrays
open function
Operating system
OR
25, 99, 105, 203
13, 203
235
4
12
61, 157
17, 235
117
101
156
235
237
82,86
11
80
168
117
213, 236
235
166
Pascal
Pointer arrays
Pointers
Precedence
Preferences
Preprocessor
4,29
189
131, 133, 173, 189, 235
61, 136
237
89, 227, 229
Preprocessor directives 229
printf 22, 25, 27, 45, 75, 98,
124, 157, 189
Keywords
25
Program format
27
putc
206
Lattice C
13, 38, 41, 46,
putchar
207
65,81,91,212
puts
189
Library macros
198
Library
25, 238
RAW
220
Linefeeds
27
Redirection
222
Linker
3, 9, 12, 27
Referencing
133
Logical AND
52
Register
143, 146, 181
Logical errors
13
return
106
Logical OR
52
<Return> key
18,40
LOGO
4
Reverse
159
long
68, 69, 82, 115,
scanf
31, 75, 131, 134,
133, 181, 182, 217
208, 218
Loops
45
Scanner
262
lseek
216
Screens
243
Semicolon
106
Machine language
4
short
68, 69, 181
Macros
3, 195, 227
sizeof
164, 191, 212
282
Abacus
Index
Smart_Refiresh
237
Source code
28, 96, 189
sprintf
220
square
106
Standard input/output
218
Statement block
34
static variables
144,
156, 181
stderr
223
stdin
223
stdio.h 91,
148,
163, 223
stdout
223
strcmp
154
strcpy 109,
135,
147, 190
Strings
57, 178
strlen
111
struct
173, 236
Structures
183, 235
switch
123, 125
Syntax errors
13
System crash
37
tell
217
text_arr
182
Tips and tricks
227
Transportability
6
Type conversion
70
typedef
178
Unbuffered input/output
213
unsigned
67,
175, 181
unsigned int
69
User-defined libraries
153
Variable declaration
105
Variables 31, 65,
, 143, 173
void
25,
105, 108
while
45, 83, 97, 98,
109,
, 123, 154
Window flags
237
windowdepth
237
windowdrag
237
windows
235
Windowsizing
237
Word processor
10
Workbench
227, 228
283
Companion Diskette
For your convenience, the program listings contained in this book are
available on an Amiga formatted floppy diskette. You should order the
diskette if you want to use the programs, but don't want to type them in from
the listings in the book.
All programs on the diskette have been fully tested. You can change the
programs for your particular needs. The diskette is available for $14.95 plus
$2.00 ($5.00 foreign) for postage and handling.
When ordering, please give your name and shipping address. Enclose a
check, money order or credit card information. Mail your order to:
5370 52nd Street SE
Grand Rapids, MI 49512
Or for fast service, call 616-698-0330.
Credit Card orders only 1-800-451-4319.
Amiga for Beginners
Vol.#1
A perfect introductory book if you're a new or prospective Amiga owner. Amiga for Beginners introduces
you to Intuition (the Amiga's graphic interface), the mouse, windows, the versatile CLI. This first volume
in our Amiga series explains every practical aspect of the Amiga in plain English. Clear, step-by-step
instructions for common Amiga tasks. Amiga for Beginners is all the info you need to get up and running.
Amiga for
Beginners
Topics include:
Unpacking and connecting the Amiga components
Starting up your Amiga
Customizing the Workbench
Exploring the Extras disk
Taking your first step in AmigaBASIC programming language
AmigaDOS functions
Using the CLI to perform "housekeeping" chores
First Aid, Keyword, Technical appendixes
Glossary
ISBN 1-55755-021-2. Suggested retail price: $16.95
Companion Diskette not available for this book.
Amiga BASIC: Inside and Out
Vol.#2
Amiga BASIC: Inside and Out is the definitive step-by-step guide to programming the Amiga in BASIC.
This huge volume should be within every Amiga user's reach. Every Amiga BASIC command is fully
described and detailed. In addition, Amiga BASIC: Inside and Out is loaded with real working programs.
AmigaBASIC
A complete guide to learning
and applying AmigaBASIC
BEEP 11 iClROEl
LJ&*
1 NEXT H \ **
ffliil!!'
IM l 11
lwu/f-M\0PBl|
/
Topics include:
Video titling for high quality object animation
Bar and pie charts
Windows
Pull down menus
Mouse commands
Statistics
Sequential and relative files
Speech and sound synthesis
ISBN 0-916439-87-9. Suggested retail price: $24.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to run! Saves you hours of typing
in program listings. Available only from Abacus. $14.95
See your local dealer or order TOLL FREE 1-800-451-4319 in US & Canada I
Amiga 3D Graphic Programming in BASIC
Vol.#3
Amiga 3D Graphic Programming in BASIC- shows you how to use the powerful graphics capabilities
of the Amiga. Details the techniques and algorithm for writing three dimensional graphics programs: ray
tracing in all resolutions, light sources and shading, saving graphics in IFF format and more.
Topics include:
• Basics of ray tracing
• Using an object editor to enter three-dimensional objects
• Material editor for creating parameters of color, shading
and mirroring of objects
• Automatic computation in different resolutions
• Using any Amiga resolution (low-res, high-res, interlace, HAM)
• Different light sources and any active pixel
• Save graphics in IFF format for later recall into any
IFF compatible drawing program
• Mathematical basics for the non-mathematician
ISBN 1-55755-044-1. Suggested retail price: $19.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to run! Saves you hours of typing
in program listings. Available only from Abacus. $14.95
Amiga Machine Language
Vol.#4
Amiga Machine Language introduces you to 68000 machine language programming presented in clear,
easy to understand terms. If you're a beginner, the introduction eases you into programming right away.
If you're an advanced programmer, you'll discover the hidden powers of your Amiga. Learn how to access
the hardware registers, use the Amiga libraries, create gadgets, work with Intuition and more.
• 68000 microprocessor architecture
• 68000 address modes and instruction set
• Accessing RAM, operating system and multitasking capabilities
• Details the powerful Amiga libraries for access to AmigaDOS
• Simple number base conversions
• Text input and output - Checking for special keys
• Opening CON: RAW: SER: and PRT: devices
• Menu programming explained
• Speech utility for remarkable human voice synthesis
• Complete Intuition demonstration program including
Proportional, Boolean and String gadgets
ISBN 1-55755-025-5. Suggested retail price: $19.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to run! Saves you hours of typing
in program listings. Available only from Abacus. $14.95
See your local dealer or order TOLL FREE 1-800-451-4319 in US & Canada
i
Amiga System Programmer's Guide
Vol.#6
Amiga System Programmer's Guide is a comprehensive guide to what goes on inside the Amiga in a
single volume. Explains in detail the Amiga chips (68000, CIA, Agnus, Denise, Paula) and how to access
them. All the Amiga's powerful interfaces and features are explained and documented in a clear precise
manner.
Topics include:
EXEC Structure
Multitasking functions
I/O management through devices and I/O request
Interrupts and resource management
RESET and its operation
DOS libraries
Disk management
Detailed information about the CLI and its commands
Much more— over 600 pages worth
ISBN 1-55755-034-4. Suggested retail price: $34.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to runl Saves you hours of typing
in program listings. Available only from Abacus. $14.95
Advanced System Programmer's Guide
Vol.#7
Advanced System Programmer's Guide for the Amiga - The second volume to our 'system
programming' book. References all libraries, with basis and primitive sturctures. Devices: parallel, serial,
printer, keyboard, gameport, input, console, clipboard, audio, translator, and timer trackdisk.
Some of the topics include:
• Interfaces- audio, video RGB, Centronics, serial,
disk access, expansion port, and keyboard
• Programming hardware- memory organization, interrupts,
the Copper, blitter and disk controller
• EXEC structures- Node, List, Libraries and Tasks
• Multitasking- Task switching, intertask communication,
exceptions, traps and memory management
• I/O- device handling and requests
• DOS Libraries- functions, parameters and error messages
• CLI- detailed internal design descriptions
ISBN 1-55755-047-6. Suggested retail price: $34.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and readyto runl Saves you hours of typing
in program listings. Available only from Abacus. $14.95
See your local dealer or order TOLL FREE 1-800-451-4319 in US & Canada
AmigaDOS: Inside & Out
Revised for 2.0
Vol.#8
AmigaDOS: Inside & Out covers the insides of AmigaDOS from the internal design up to practical
applications. AmigaDOS inside & Out will show you how to manage Amiga's multitasking capabilities
more effectively. There is also a detailed reference section which helps you find information in a flash, both
alphabetically and in command groups. Topics include: Getting the most from the AmigaDOS Shell
(wildcards and command abbreviations) • Script (batch) files - what they are and how to write them.
More topics include:
• AmigaDOS - Tasks and handling
• Detailed explanations of CLI commands and their functions
• In-depth guide to ED and EDIT
• Amiga devices and how the AmigaDOS Shell uses them
• Customizing your own startup-sequence
• AmigaDOS and multitasking
• Writing your own AmigaDOS Shell commands in C
• Reference for 1 .2, 1 .3 and 2.0 commands
ISBN 1-55755-041-7. Suggested retail price: $19.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to run! Saves you hours of typing
in program listings. Available only from Abacus. $14.95
Amiga Disk Drives: Inside & Out
Vol.#9
Amiga Disk Drives: Inside & Out shows everything you need to know about Amiga disk drives. You'll
find information about data security, disk drive speedup routines, disk copy protection, boot blocks,
loading and saving programs, sequential and relative file organization and much more.
Topics include:
• Floppy disk operations from the Workbench and CLI
• DOS functions and operations
• Disk block types, boot blocks, checksums, file headers,
hashmarks and protection methods
• Viruses and how to protect your boot block
• Trackdisk device: Commands and structures
• Trackdisk-task: Function and design
• MFM, GCR, track design, blockheader, datablocks, coding
and decoding data, hardware registers, SYNC and interrupts
ISBN 1-55755-042-5. Suggested retail price: $29.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to run! Saves you hours of typing
in program listings. Available only from Abacus. $14.95
See your local dealer or order TOLL FREE 1-800-451-4319 in US & Canada I
Amiga C for Beginners
Vol.#10
Amiga C for Beginners is an introduction to learning the popular C language. Explains the language ele-
ments using examples specifically geared to the Amiga. Describes C library routines, how the compiler
works and more.
Topics include:
• Beginner's overview of C
• Particulars of C
• Writing your first program
• The scope of the language (loops, conditions, functions,
structures)
• Special features of the C language
• Input/Output using C
• Tricks and Tips for finding errors
• Introduction to direct programming of the operating system
(windows, screens, direct text output, DOS functions)
Using the LATTICE and AZTEC C compilers
ISBN 1-55755-045-X. Suggested retail price: $19.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to runl Saves you hours of typing
in program listings. Available only from Abacus. $14.95
Amiga C for Advanced Programmers
Vol.#11
Amiga C for Advanced Programmers contains a wealth of information from the C programming pros:
how compilers, assemblers and linkers work, designing and programming user friendly interfaces utilizing
the Amiga's built-in user interface Intuition, managing large C programming projects, using jump tables
and dynamic arrays, combining assembly language and C codes, using MAKE correctly. Includes the
complete source code for a text editor.
Topics include:
• Using INCLUDE, DEFINE and CAST
• Debugging and optimizing assembler sources
• Ail about programming Intuition including windows, screens,
pulldown menus, requesters, gadgets and more
• Programming the console device
• A professional editor's view of problems with developing
larger programs
• Debugging C programs with different utilities
ISBN 1-55755-046-8. Suggested retail price: $34.95
Companion Diskette available: Contains every program listed in the
book- complete, error free and ready to run! Saves you hours of typing
in program listings. Available only from Abacus. $14.95
See your local dealer or order TOLL FREE 1-800-451-4319 in US & Canada
AmigaDOS Quick Reference
AmigaOOS Quick Reference is an easy-to-use reference tool for beginners and advanced programmers
alike. You can quickly find commands for your Amiga by using the three handy indexes designed with the
user in mind. All commands are in alphabetical order for easy reference. The most useful information you
need fast can be found including:
• All AmigaDOS commands described with examples including
Workbench 1 .3
• Command syntax and arguments described with examples
• CLI shortcuts
• CTRL sequences
• ESCape sequences
• Amiga ASCII table
• Guru Meditation Codes
• Error messages with their corresponding numbers
Three indexes for instant information at your fingertips! The
AmigaDOS Quick Reference is an indispensable tool you'll want
to keep close to your Amiga.
ISBN 1-55755-049-2. Suggested retail price: $9.95
Companion Diskette not available for this book.
Abacus Amiga Book Summary
Vol.1
Amiga for Beginners
1-55755-021-2
$16.95
Vol.2
AmigaBASIC: Inside and Out
0-916439-87-9
$24.95
Vol.3
Amiga 3D Graphic Programming in BASIC
1-55755-044-1
$19.95
Vol.4
Amiga Machine Language
1-55755-025-5
$19.95
Vol.6
Amiga System Programmers Guide
1-55755-034-4
$34.95
Vol.7
Advanced System Programmers Guide
1-55755-047-6
$34.95
Vol.8
AmigaDOS: Inside and Out
1-55755-041-7
$19.95
Vol.9
Amiga Disk Drives: Inside and Out
1-55755-042-5
$29.95
Vol.10
'C for Beginners
1-55755-045-X
$19.95
Vol.11
'C for Advanced Programmers
1-55755-046-8
$24.95
Vol.13
Amiga Graphics: Inside & Out
1-55755-052-2
$34.95
Vol.14
Amiga Desktop Video Guide
1-55755-057-3
$19.95
Vol.15
Amiga Printers: Inside & Out w/ disk
1-55755-087-5
$34.95
Vol.16
Making Music on the Amiga w/disk
1-55755-094-8
$34.95
Vol.17
Best Amiga Tricks & Tips w/ disk
1-55755-107-3
$29.95
AmigaDOS Quick Reference
1-55755-049-2
$9.95
See your local dealer or order TOLL FREE 1-800-451-4319 in US & Canada I
Amiga Graphics Inside & Out
The Amiga Graphics Inside & Out book will show you simply and in plain Eng-
lish Ihe super graphic features and functions of the Amiga in detail. You will
learn the graphic features that can be accessed from AmigaBASIC or C.
The advanced user will learn graphic programming in C with examples of
points, lines, rectangles, polygons, colors and more. Amiga Graphics
Inside & Out contains a complete description of the Amiga graphic
system - View, Viewport, RaslPort, bitmap mapping, screens, and
windows.
Topics include:
«V**
Accessing fonts and type styles in AmigaBASIC
CAD on a 1024 x 1024 super bitmap, Using graphic
library routines
New ways to access libraries and chips from BASIC - 4096
colors at once, color patterns, screen and window dumps to printer
Graphic programming in C - points, lines, rectangles, polygons.colors
Amiga animation explained including sprites, bobs and AnimObs, Copper and blitter programming
Volume 13 Suggested retail price $34.95 ISBN 1-55755-052-2
GLN
j Optional Diskette $14.95 #727
GLN
Amiga Desktop Video Guide
The Amiga Desktop Video Guide is the most complete and useful guide to desktop video on the Amiga.
Amiga Desktop Video Guide covers all the basics - defining video terms,
selecting genlocks, digitizers, scanners, VCRs, camera and connecting
them to the Amiga.
Just a few of the topics you'll find described in this excellent book:
The Basics ol Video
Genlocks
Digitizers and Scanners
Frame Grabbers/Frame Buffers
How to connect VCRs, VTRs, and Cameras to the Amiga
Animation
Video Titling
Music and Videos
Home Video
Advanced Techniques
Using the Amiga to add or incorporate Special Effects to a video
Tips on Paint, Ray Tracing, and 3-D Rendering in Commercial Applications
Volume 14 • Suggested Retail Price $19.95 • ISBN 1-55755-057-3
Save Time and Moneyl-Optional program disks are available for all our Amiga reference
books (except Amiga for Beginners and AmigasDOS Quick Reference). Programs listed in
the book are on each respective disk and saves countless hours of typing! $14.95
Books for the AMIGA
IWWIIII
AmigaDOS Quick Reference Guide
AmigaDos Quick Reference Guide is an easy-to-use reference tool for
beginners and advanced programmers alike. You can quickly find commands
for your Amiga by using the three handy indexes designed with the user in
mind. All commands are in alphabetical order for easy reference. The most
useful information you need fast can be found- including:
• All AmigaDOS commands described, including Workbench 1 .3
• Command syntax and arguments described with examples
• CLI shortcuts
• CTRL sequences
• ESCape sequences
• Amiga ASCII table
■ Guru Meditation Codes
• Error messages with their corresponding numbers j
Three indexes for quick information at your fingerlipsl The AmigaDOS
Quick Reference Guide is an indispensable tool you'll want to keep close
to your Amiga.
Suggested retail price US $9.95 ISBN 155755-049-2
Abacus Amiga
Books
Vol. 1
Amiga for Beginners
1-55755-021-2
$16.95
Vol. 2
AmigaBASIC Inside & Out
0-916439-87-9
$24.95
Vol. 3
Amiga 3D Graphic Programming in BASIC
1-55755-044-1
$19.95
Vol. 4
Amiga Machine Lanquaqe
1-55755-025-5
$19.95
Vol. 5
Amiqa Tricks & Tips
0-916439-88-7
$19.95
Vol. 6
Amiqa System Proqrammers Guide
1-55755-034-4
$34.95
Vol. 7
Advanced System Proqrammers Guide
1-55755-047-6
$34.95
Vol. 8
AmiqaDOS Inside & Out
1-55755-041-7
$19.95
Vol. 9
Amiga Disk Drives Inside & Out
1-55755-042-5
$29.95
Vol. 10
Amiqa C for Beqinners
1-55755-045-X
$19.95
Vol. 11
Amiga C for Advanced Proqrammers
1-55755-046-8
$34.95
Vol. 12
More Tricks & Tips for the Amiqa
1-55755-051-4
$19.95
Vol. 13
Amiqa Graphics Inside & Out
1-55755-052-2
$34.95
Vol. 14
Amiqa Desktop Video Guide
1-55755-057-3
$19.95
AmiqaDOS Quick Reference Guide
1-55755-049-2
$ 9.95
Abacus Products for Amiga computers
Professional DataRetrieve
The Professional Level
Database Management System
Professional DataRetrieve, for the Amiga 500/1000/2000,
is a friendly easy-to-opcrate professional level data manage-
ment package with the features most wanted in a relational
data base system.
Professional DataRetrieve has complete relational data
mangagement capabilities. Define relationships between
different files (one to one, one to many, many to many).
Change relations without file reorganization.
Professional DataRetrieve includes an extensive program-
ming laguage which includes more than 200 BASIC-like
commands and functions and integrated program editor.
Design custom user interfaces with pulldown menus, icon
selection, window activation and more.
Professional DataRetrieve can perform calculations and
searches using complex mathematical comparisons using
over 80 functions and constants.
Professional DataRetrieve is a friendly, easy to operate
programmable RELATIONAL data base system. PDR in-
cludes PROFIL, a programming language similar to BASIC.
You can open and edit up to 8 flics simultaneously and Ihe
size of your data fields, records and files are limited only by
your memory and disk storage. You have complete interre-
lation between files which can include IFF graphics. NOT
COPY PROTECTED. ISBN 1-55755-048-4
MORE features of Professional DataRetrieve
Easily import data from other databascs....file compatible
with standard DataRetrieve....supportsmultitasking...design
your own custom forms with the completely integrated
printer mask cditor....includcs PROFIL programming lan-
guage that allows the programmer to custom tailor his data-
base requirements...
MORE features of PROFIL include:
Open Amiga devices including the console, printer,
serial and the CLI.
Create your own programmable requestors
Complete error trapping.
Built-in compiler and much, much more.
Suggested retail price:
$295.00
PROFESSIONAL
DataRetrieve
The
Professional
level
Database.*
Features
• Up to 8 files can be edited simultaneously
■ Maximum size of a data field 32,000 characters
(text fields only)
• Maximum number of data fields limited by RAM
• Maximum record size of 64,000 characters
• Maximum number of records disk dependent
(2,000,000,000 maximum)
• Up to 80 index fields per file
• Up to 6 field types - Text, Date, Time, Numeric,
IFF, Choice
• Unlimited number of searches and subrange
criteria
• Integrated list editor and full-page printer mask
editor
• Index accuracy selectable from 1-999 characters
■ Multiple file masks on-screen
• Easily create/edit on-screen masks for one or
many files
• User-programmable pulldown menus
• Operate the program from the mouse or the key
board
■ Calculation fields, Data Fields
IFF Graphics supported
• Mass-storage-oriented file organization
• Not Copy Protected, NO DONGLE; can be in
stalled on your hard drive
Selected Abacus Products for the Amiga computers
BeckerText
Powerful Word Processing
Package for the Amiga
BeckerText Amiga is more than just a word processor.
BeckerText Amiga gives you all of the easy-to-use
features found in our TextPro Amiga, plus it lets you
do a whole lot more. You can merge sophisticated IFF-
graphics anywhere in your document You can hyphenate,
create indexes and generate a table of contents for your
documents, automatically. And what you see on the
BeckerText screen is what you get when you print the
document— real WYSIWYG formatting on your Amiga.
But BeckerText gives you still more: it lets you
perform calculations of numerical data within your
documents, using flexible templates to add, subtract,
multiply and divide up to five columns of numbers on a
page. BeckerText can also display and print multiple
columns of text, up to five columns per page, for
professional-looking newsletters, presentations, reports,
etc. Its expandable built-in spell checker eliminates those
distracting typographical errors.
BeckerText works with most popular dot-matrix and
letter-quality printers, and even the latest laser printers for
typeset-quality output. Includes comprehensive tutorial
and manual.
BeckerText gives you the power and flexibility that you
need to produce the professional-quality documents that
you demand.
When you need more from your word processor than just
word processing, you need BeckerText Amiga.
Discover the power of BeckerText.
Suggested retail price:
$150.00
Features
Select options from pulldown menus or handy shortcut
keys
Fast, true WYSIWYG formatting
Bold, italic, underline, superscript and subscript
characters
Automatic wordwrap and page numbering
Sophisticated tab and indent options, with centering and
margin justification
Move, Copy, Delete, Search and Replace
Automatic hyphenation, with automatic table of
contents and index generation
Write up to 999 characters per line with horizontal
scrolling feature
Check spelling as you write or interactively proof
document; add to dictionary
Performs calculations within your documents —
calculate in columns with flexible templates
Customize 30 function keys to store often-used text
and macro commands
Merge IFF graphics into documents
Includes BTSnap program for converting text blocks to
IFF graphics
C-source mode for quick and easy C language program
editing
Print up to 5 columns on a single page
Adapts to virtually any dot-matrix, letter-quality or laser
printer
Comprehensive tutorial and manual
Not copy protected
Selected Abacus Products for the Amiga computers
AssemPro
Machine Language Development
System for the Amiga
Bridge the gap between slow higher-level languages and
ultra-fast machine language programming: AssemPro
Amiga unlocks the full power of the AMIGA'S 68000
processor. It's a complete developer's kit for rapidly
developing machine language/assembler programs on
your Amiga. AssemPro has everything you need to write
professional-quality programs "down to the metal":
editor, debugger, disassembler & reassembler.
Yet AssemPro isn't just for the 6S000 experts.
AssemPro is easy to use. You select options from the
dropdown menus or with shortcut keys, which makes
your program development a much simpler process. With
the optional Abacus book Amiga Machine Language (see
page 3), AssemPro is the perfect introduction to Amiga
machine language development and programming.
AssemPro also has the professional features that
advanced programmers look for. Lots of "extras"
eliminate the most tedious, repetitious and time-
consuming m/1 programming tasks. Like syntax error
search/replace functions to speed program alterations and
debugging. And you can compile to memory for lighting
speed. The comprehensive tutorial and manual have the
detailed information you need for fast, effective
programming.
AssemPro Amiga offers more professional features,
speed, sheer power, and ease of operation than any other
assembler package we've seen for the money. Test drive
your AssemPro Amiga with the security of the Abacus
30-day guarantee.
Suggested retail price: $99.95
Features
Integrated Editor, Debugger, Disassembler and
Reassembler
Large operp'ing system library
Runs under CLI and Workbench
Produces either PC-relocatable or absolute code
Create custom macros for nearly any parameter (of
different types)
Error search and replace functions
Cross-reference list
Menu-controlled conditional and repeated assembly
Full 32-bit arithmetic
Advanced debugger with 68020 single-step emulation
Written completely in machine language for ultra-fast
operation
Runs on any Amiga with 512K or more and Kickstart
version 1.2
Not copy protected
Machine language programming requires a solid understanding
of the AMIGA s hardware ana operating system. We do not
recommend this package to beginning Amiga programmers
Abacus Products for Amiga computers
DataRetrieve
A Powerful Database Manager
for the Amiga
Imagine a powerful database for your Amiga: one that's
fast, has a huge data capacity, yet is easy to work with.
Now think DataRetrieve Amiga. It works the same
way as your Amiga — graphic and intuitive, with no
obscure commands. You quickly set up your data files
using convenient on-screen templates called masks. Select
commands from the pulldown menus or time-saving
shortcut keys. Customize the masks with different text
fonts, styles, colors, sizes and graphics. If you have any
questions, Help screens are available at the touch of a
button. And DataRetrieve's 128-page manual is clear
and comprehensive.
DataRetrieve is easy to use — but it also has
professional features for your most demanding database
applications. Password security for your data.
Sophisticated indexing with variable precision. Full
Search and Select functions. File sizes, data sets and data
fields limited only by your memory and disk storage
space. Customize up to 20 function keys to store macro
commands and often-used text. For optimum access speed,
DataRetrieve takes advantage of the Amiga's multi-
tasking.
You can exchange data with TextPro Amiga,
BeckerText Amiga and other packages to easily
produce form letters, mailing labels, index cards,
bulletins, etc. DataRetrieve prints data reports to most
dot-matrix & letter-quality printers.
DataRetrieve is the perfect database for your Amiga.
Get this proven system today with the assurance of the
Abacus 30-day MoneyBack Guarantee.
Suggested retail price:
$79.95
Features
Select commands and options from the pulldown menus
or shortcut keys
Enter data Into convenient screenmasks
Enhance screen masks with different text styles, fonts,
colors, graphics, etc.
Work with 8 databases concurrently
Define different field types: text, date, time, numeric &
selection
Customize 20 function keys to store macro commands
and text
Specify up to 80 index fields for superfast access to
your data
Perform simple or complex data searches
Create subsets of a larger database for even faster
operation
Exchange data with other packages: form letters,
mailing lists etc.
Produce custom printer forms: Index cards, labels,
Rolodex-cards, etc. Adapts to most dot-matrix & letter-
quality printers
Protect your data with passwords
Get Help from online screens
Not copy protected
Max. file size
Max. data record size
Max. data set . ,
Max. no. of data fields «™ dlsk s P aca
Max. field size
Limited only
by your memory
Presenting...
A collection of
essential, powerful,
and easy-to-use tools
for your Amiga.
Here's a new software package
that every Amiga owner can use.
Abacus' AmigaDOS Toolbox
has the tools you need to make
your Amiga computing easier
and more productive. Whether
you are a beginner or an advanced
Amiga user you'll find the
AmigaDOS Toolbox to be just
what you've been looking for.
To order call Toll Free 1-800-451 -431 9
Abacus!
Dept. L5, 5370 52nd Street S.E.
Grand Rapids, Ml 49512
Phone:(616)698-0330
Some of our best tools included are:
• DeepCopy- one of the fastest
FULL disk copiers; copies many
different formats.
• Speeder- a data speedup utility
(more than 300%) -not a disk cache.
• BTSnap- a screen grabber deluxe.
• Diskmon- a full-featured disk
editing tool.
• Fonts- eleven new originals you
can use in your Amiga text.
...and many additional tools that
every Amiga owner can use.
Bought individually, equivalent
software could cost up to $200.
Amiga and AmigaDOS are registered trademarks d Commodore-Amiga Inc.
Presenting.
Protect your Amiga computer
system with this collection of
essential and valuable tools!
a sir
IjMffE
Jc^S^'if^
a
Includes I
Computer y* _ ,/ « s^s^lMfcyilll
Viruses!
* $59.95
AN
The Virus Protection Toolbox
describes how computer viruses
work; what problems viruses
cause; how viruses invade the
Libraries, Handler and Devices
of the operating system;
preventive maintenance; how to
cure infected programs and disks.
Works with Workbench 1.2 and 1.3!
Abacus!
5370 52nd Street S.E.
Grand Rapids, Ml 49512
Available at your local dealer or
Order Toll Free 1-800-451-4319
Amiga Is a registered trademark of Commodore-Amiga Inc.
Some of our best tools included are:
• Boot Check-
to prevent startup viruses.
• Recover-
to restore the system information
to disk.
• Change Control Checker-
to record modifications to
important files.
• Check New-
to identify new program and data files.
Order now or call for your Free
pamphlet "What you should know
about Computer Viruses"
(while supplies last)
programming language of choice for
Amiga users worldwide. Amiga C for
Beginners is an introductory guide for the
Amiga user who wants to learn and
understand this popular language. He'll
learn the basic and intermediate
programming techniques and without a lot
of technical jargon! Amiga C for
Beginners shows you in plain English the
language elements using examples
specifically tailored to the Amiga.
Amiga C for Beginners explains the basic
structure and peculiarities of each C
statement and function. And it shows the
user how to use many of the features of the
Amiga's operating system - windows,
screen, text output, DOS functions and
more. Amiga C for Beginners gives you all
you need to immediately start programming
in C with your Amiga.
Amiga C for Beginners describes C
library routines - C language structures -
how a C compiler works - using C with
your Amiga and much, much more.
US$19.95
ISBN 1-5575!
9 78155P5
learning and using
C on your Amiga
Topics include:
• Beginner's overview of C
• Writing your first C program
• Special features of the C language
• Important routines in the C libraries
• Input and Output using C
• The scope of the C language revealed
(loops, conditions, functions, structures)
• Tricks & Tips for finding errors
• Using two of the most popular C compilers
• And much more
Optional Program Diskette available:
Contains every program listed in the book-
complete, error-free and ready to run! Saves
you hours of typing in the programs.
Abacu
unman
BfflfM
5370 52nd Street SE, Grand Rapids, Ml 49512
is a iegisiered trademark el Commodore- Amiga inc
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